Warwick Mathematics Institute Events
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Upcoming Seminars

Combinatorics on 10 November 2023 at 14:00 in B3.02
Speaker: Tom Johnston (Bristol)
Title: Shotgun assembly of random graphs
Abstract: TBA

Colloquium on 10 November 2023 at 16:00 in B3.02
Speaker: Rob Hollingworth, Tom MontenegroJohnson, Randa Herzallah (Warwick)
Title: Impact  what it is, how it's done, and why it's good for you
Abstract: Impact is about how academics reach out to the wider world. This can arise through working with industry, local or national agencies, or through public understanding and involvement. The success of the Maths Institute in the next REF assessment will be critically dependent on both specific Impact Case Studies and the general role of impact within the department.
This threepart talk will explain what Impact is and what it means to the Maths Institute, it will inform about how you can get involved with Impact activities and what this means for you, and it will give one (or two depending on time) examples of Impact Case studies. The colloquium will specifically address topics of relevance for those at the start of their own impact journey (or who may not even know how impactful their activities could be!). 
Junior Analysis and Probability Seminar on 13 November 2023 at 15:00 in D1.07
Speaker: Zofia Grochulska (Warsaw)
Title: Homeomorphisms with (approximate) derivative
Abstract: Homeomorphisms of subsets of R^n can be used to model deformations such as stretching a rubber band or bending a metal plate. This is one of the reasons why there has been an interest in studying homeomorphisms equipped with some notion of differentiability. I will talk mainly about almost everywhere (a.e.) approximately differentiable homeomorphisms and the interplay between their analytical and topological properties and discuss if these properties might be useful for potential applications. In particular, we will see that under mild assumptions on T, a measurable map defined on a unit cube in R^n with values in the space of invertible n x n matrices, there is an a.e. approximately differentiable homeomorphism of the unit cube whose approximate derivative equals T a.e. I will also show how closely this theorem is connected with the Homeomorphic measures theorem of Oxtoby and Ulam. This is joint work with Paweł Goldstein (University of Warsaw) and Piotr Hajłasz (University of Pittsburgh).

Algebra on 13 November 2023 at 17:00 in B3.02
Speaker: Peiran Wu (University of St Andrews)
Title: Irredundant bases for the symmetric and alternating groups
Abstract: An irredundant base of a group G acting faithfully on a finite set Γ is a sequence of points in Γ that produces a strictly descending chain of pointwise stabiliser subgroups in G, terminating at the trivial subgroup. I will give an overview of known results about the irredundant base size, before focusing on the case where G is the symmetric or alternating group of degree n with a nonstandard primitive action. It was proved in 2011 that an irredundant base of size 2 exists for such an action in all but finitely many cases. I will speak about the recent work by me and my supervisor, where we have shown that the maximum size of an irredundant base for the action is O(√n) and in most cases O((log n)^2). These upper bounds are also best possible in their respective cases, and I will present some interesting examples constructed to prove their optimality.

Algebraic Topology on 14 November 2023 at 16:00 in B3.03
Speaker: Kaif Hilman (Max Planck Institute Bonn)
Title: Equivariant hermitian Ktheory and a periodicity result for C_2Ltheory
Abstract: Building upon the recent foundational advances in hermitian Ktheory by a set of nine authors and the formalism of parametrised higher categories by a set of five authors, I will introduce in this talk a Gequivariant enhancement of the hermitian theory via the notion of a GPoincare category for finite groups G. As an application, I will indicate how one can use said enhancement to deduce a new periodicity result for Ltheory when G is the cyclic group of order 2.

Geometry and Topology on 16 November 2023 at 14:00 in B3.02
Speaker: Sam Hughes (University of Oxford)
Title: TBA
Abstract: TBA

Analysis on 16 November 2023 at 16:00 in B3.02
Speaker: Carlo Gasparetto (Pisa)
Title: A Viscosity and Monotonicity Approach to EpsilonRegularity
Abstract: Allard’s theorem states that a minimal surface that is close enough to a plane coincides with the graph of a smooth function which enjoys suitable apriori estimates. In this talk I show how to prove this result and its parabolic counterpart by exploiting viscosity techniques and a weighted monotonicity formula. Based on a joint work with G. De Philippis and F. Schulze.

Mathematics Teaching and Learning on 16 November 2023 at 16:00 in MS.05
Speaker: Martyn Parker (Warwick Statistics)
Title: QAA subject benchmark statements for Mathematics, Statistics and Operational Research
Abstract: In this talk I will discuss the Subject Benchmarking Statements (SBS) for Mathematical Sciences and Operational Research (MSOR). Subject Benchmark Statements describe the nature of study and the academic standards expected of graduates in MSOR. They show what graduates might reasonably be expected to know, do and understand at the end of their studies.
The benchmarking statements are creating and updated by members of the MSOR community under the guidance of the QAA (Quality Assurance Agency for Higher Education). The most recent MSOR updates took place over a period of approximately 1 year and were published in 2023.
I will discuss the interface between the HE regulator, the Office for Students (OfS), and the SBS statements. In particular, how the current OfS regulatory framework and requirements interact with SBS updates. 
Partial Differential Equations and their Applications on 21 November 2023 at 12:00 in B3.02
Speaker: Mattia Zanella (Univ. Pavia)
Title: TBA
Abstract: TBA

Geometry and Topology on 23 November 2023 at 14:00 in B3.02
Speaker: Jeffrey Giansiracusa (Durham University)
Title: TBA
Abstract: TBA

Geometry and Topology on 30 November 2023 at 14:00 in B3.02
Speaker: Cameron Gates Rudd (MPI Bonn)
Title: TBA
Abstract: TBA

Combinatorics on 08 December 2023 at 14:00 in B3.02
Speaker: Ryan Martin (Iowa State)
Title: Counting cycles in planar graphs
Abstract: TBA

Statistical Mechanics on 09 November 2023 at 16:00
Speaker: Laurent Thomann (Université de Lorraine)
Title: Almost sure scattering for the one dimensional nonlinear Schrödinger equation
Abstract: We exhibit measure on the space of initial data for which we describe the non trivial evolution by the linear Schrödinger flow and we show that their nonlinear evolution is absolutely continuous with respect to this linear evolution. Actually, we give precise (and optimal) bounds on the RadonNikodym derivatives of these measures with respect to each other and we characterise their L^p regularity. We deduce from this precise description the global wellposedness of the equation for p>1 and scattering for p>3. This is joint work with Nicolas Burq.

Geometry and Topology on 09 November 2023 at 14:00
Speaker: Monika Kudlinska (University of Oxford)
Title: Subgroup separability in 3manifold and freebycyclic groups
Abstract: A group G is said to be subgroup separable if every finitely generated subgroup of G is the intersection of finite index subgroups. It is known that a fundamental group of a compact, irreducible, closed 3manifold M is subgroup separable if and only if M is geometric. We will discuss the problem of subgroup separability in freebycyclic groups by drawing a parallel between freebycyclic and 3manifold groups. Time permitting, we will discuss how to extend these ideas to find nonseparable subgroups in random groups

Probability Theory on 08 November 2023 at 16:00
Speaker: Balint Toth (University of Bristol)
Title: (Towards an) Invariance Principle for the Random Lorentz Gas under Weak Coupling Limit Beyond the Kinetic Time Scale
Abstract: KestenPapanicolaou (1980) proved that in the weak coupling limit the random Lorentzgas process with soft scatterers converges to the Spherical Langevin Process. Under a second, diffusive limit the spatial component of the Spherical Langevin Process converges to Brownian motion. KomorowskiRyzhik (2006) proved that combining the weak coupling and diffusive limits, the Brownian motion is obtained, at least for a time horizon slightly beyond the kinetic timescale. We attempt to extend this last result robustly for time scales way beyond the kinetic one. (Work in progress.)

Algebraic Geometry on 08 November 2023 at 15:00
Speaker: Shengyuan Huang (Birmingham)
Title: The orbifold Hochschild product for Fermat hypersurface
Abstract: For a smooth scheme X, the Hochschild cohomology of X is isomorphic to the cohomology of polyvector fields as algebras. This result is claimed by Kontsevich and then proved by Calaque and Van den Bergh. In this talk, I will present my recent progress with Andrei Caldararu and Kai Xu in generalising the result above to orbifolds.
In the projective spaces, one can consider the Fermat hypersurfaces with natural group actions. These are the main examples that we focus on in this talk. If we further assume that the hypersurface is CalabiYau, we prove the algebra isomorphism between its Hochschild cohomology and polyvector fields. 
Algebraic Topology on 07 November 2023 at 16:00
Speaker: Scott Balchin (Queen's University Belfast)
Title: A jaunt through the tensortriangular geometry of rational G spectra for G profinite or compact Lie
Abstract: TBA

Algebraic Geometry on 07 November 2023 at 15:00
Speaker: Alicia Dickenstein (University of Buenos Aires)
Title: Iterated and mixed discriminants
Abstract: Classical work by Salmon and Bromwich classified singular intersections of two quadric surfaces. The basic idea of these results was already pursued by Cayley in connection with tangent intersections of conics in the plane and used by Schafli for the study of hyperdeterminants. More recently, the problem has been revisited with similar tools in the context of geometric modeling and a generalization to the case of two higher dimensional quadric hypersurfaces was given by Ottaviani. In joint work with Sandra di Rocco and Ralph Morrison, we propose and study a generalization of this question for systems of Laurent polynomials with support on a fixed point configuration. In the nondefective case, the closure of the locus of coefficients giving a nondegenerate multiple root of the system is defined by a polynomial called the mixed discriminant. We define a related polynomial called the multivariate iterated discriminant. This iterated discriminant is easier to compute and we prove that it is always divisible by the mixed discriminant. We show that tangent intersections can be computed via iteration if and only if the singular locus of a corresponding dual variety has sufficiently high codimension. We also study when point configurations corresponding to SegreVeronese varieties and to the lattice points of planar smooth polygons, have their iterated discriminant equal to their mixed discriminant.

Partial Differential Equations and their Applications on 07 November 2023 at 12:00
Speaker: Elaine Crooks (Swansea University)
Title: TBA
Abstract: TBA

Algebra on 06 November 2023 at 17:00
Speaker: Martin van Beek (University of Manchester)
Title: Exotic Fusion Systems Related to Sporadic Simple Groups
Abstract: Fusion systems offer a way to examine and express properties of the pconjugacy of elements in finite groups. However, not every fusion system may be constructed from a finite group in an appropriate way. This gives rise to exotic fusion systems. An important research direction involves the study of the behaviour of exotic fusion systems (in particular at odd primes).
In this talk, we describe several exotic fusion systems related to the sporadic simple groups at odd primes. More generally, we classify saturated fusion systems supported on Sylow 3subgroups of the Conway group Co1 and the Thompson group F3, and a Sylow 5subgroup of the Monster M, as well as a particular maximal subgroup of the latter two pgroups. This work is supported by computations in MAGMA. 
Junior Number Theory on 06 November 2023 at 11:00
Speaker: Alexandros Konstantinou (University College London)
Title: Unveiling the power of isogenies: From Galois theory to the Birch and SwinnertonDyer conjecture
Abstract: In this talk, we have a twofold aim. Firstly, we illustrate a method for constructing isogenies using basic Galois theory and representation theory of finite groups. By exploiting the isogenies thus constructed, we shift our focus to the second aspect of our talk: the investigation of ranks of Jacobians with emphasis on predictions made by the Birch and SwinnertonDyer conjecture. Finally, we showcase the utility of our approach for studying ranks through various applications. These include a unified framework for studying classical isogenies and ranks, as well as a new proof for the parity conjecture for elliptic curves defined over number fields. This is joint work with V. Dokchitser, H. Green and A. Morgan.

Colloquium on 03 November 2023 at 16:00
Speaker: Henna Koivusalo (Bristol)
Title: The tales of aperiodic order
Abstract: Aperiodic order is at most loosely term to describe discrete point sets (or tilings), which have no translational period but feature some signs of longrange organisation. The tale of the study of aperiodic order is fundamentally intertwined with physics, but as a field of mathematics also lies in the deep shadow of logic. My take on this story will cover the past 60odd years in approximate chronological order, beginning with first examples of aperiodic tilesets, the Nobel prizewinning discovery of quasicrystal materials, and the quest to find wild quasicrystals, and ending with the unbelievable story, from just earlier this year, of finding the first aperiodic monotile.
Time permitting, I will explain in further detail some results on my favourite method for producing aperiodic order, the cut and project sets, which are obtained by taking an irrational slice through a lattice and projecting it to a lower dimensional subspace. The definition of cut and project sets allows for many interpretations and generalisations, and they can naturally be studied in the context of dynamical systems, discrete geometry, harmonic analysis, or Diophantine approximation, for example, depending on one's own tastes and interests. 
Mathematics Teaching and Learning on 02 November 2023 at 16:00
Speaker: Sue JohnstonWilder (Warwick Education Studies)
Title: 90% of jobs need maths; 30% of the population has maths anxiety: what can we do?
Abstract: I will seek to raise awareness of maths anxiety, how it affects an average 30% of the people around you at the University of Warwick and in the wider community and how you can begin to become part of the solution.
I will introduce notions of prior harm, psychological safety and resilience applied to learning mathematics and share the mathematical resilience toolkit, showing how it is being adopted in several countries around the world. 
Statistical Mechanics on 02 November 2023 at 16:00
Speaker: Igor Wigman (King's College London)
Title: Almost sure GOE fluctuations of energy levels for hyperbolic surfaces of high genus
Abstract: Title:
This talk is based on a joint work with Zeev Rudnick.
We study the variance of a linear statistic of the Laplace eigenvalues on a hyperbolic surface, when the surface varies over the moduli space of all surfaces of fixed genus, sampled at random according to the WeilPetersson measure. The ensemble variance of the linear statistic was recently shown to coincide with that of the corresponding statistic in the Gaussian Orthogonal Ensemble (GOE) of random matrix theory, in the double limit of first taking large genus and then shrinking size of the energy window. We show that in this same limit, the energy variance for a typical surface is close to the GOE result, a feature called "ergodicity" in the random matrix theory literature. 
Analysis on 02 November 2023 at 16:00
Speaker: Dario Prandi (ParisSaclay)
Title: Weyl's law for singular Riemannian manifolds
Abstract: We will discuss some new results relating to the asymptotic growth of the eigenvalues of the LaplaceBeltrami operator on Riemannian manifolds. In particular, we will focus on a singular setting, where all geometrical invariants appearing in classical spectral asymptotics are unbounded, and the total volume can be infinite. In this setting, under suitable assumptions on the curvature blowup, we will show how the singularity influences the Weyl's asymptotics and how to construct singular Riemannian metrics with prescribed nonclassical Weyl's law. A key tool in our arguments is a new quantitative estimate for the remainder of the heat trace and the Weyl's function on Riemannian manifolds, which is of independent interest.
This is a joint work with Yacine Chitour (Univ. ParisSaclay, France) and Luca Rizzi (SISSA, Trieste, Italy). 
Geometry and Topology on 02 November 2023 at 14:00
Speaker: Adele Jackson (University of Oxford)
Title: Algorithms for Seifert fibered spaces
Abstract: Given two mathematical objects, the most basic question is whether they are the same. We will discuss this question for triangulations of threemanifolds. In practice there is fast software to answer this question and theoretically the problem is known to be decidable. However, our understanding is limited and known theoretical algorithms could have extremely long runtimes. I will describe a programme to show that the 3manifold homeomorphism problem is in the complexity class NP, and discuss the important subcase of Seifert fibered spaces.

Probability Theory on 01 November 2023 at 16:00
Speaker: Erlend Grong (University of Bergen)
Title: SubRiemannian geometry, most probable paths and transformations.
Abstract: Hello Everyone,
This week's Probability Seminar speaker will be Erlend Grong from the University of Bergen. The talk will take place in B3.03 on Wednesday, November 1, 1617. The title and abstract, as well as the MS Teams link for the talk are given below.
Best regards,
Vedran and Giuseppe
Doing statistics on a Riemannian manifold becomes very complicated for the reason that we lack tools to define such things as mean and variance. Using the Riemannian distance, we can define a mean know as the Fréchet mean, but this gives no concept of asymmetry, also known as anisotropy. We introduce an alternative definition of mean called the diffusion mean, which is able to both give a mean and the analogue of a covariance matrix for a dataset on a Riemannian manifolds.
Surprisingly, computing this mean and covariance is related to subRiemannian geometry. We describe how subRiemannian geometry can be applied in this setting, and mention some finite dimensional and infinitedimensional applications.
The results are part of joint work with Stefan Sommer (Copenhagen, Denmark). 
Algebraic Geometry on 01 November 2023 at 15:00
Speaker: Marvin Anas Hahn (Trinity College Dublin)
Title: Mustafin degenerations of syzygy bundles
Abstract: Mustafin varieties are degenerations of projective spaces, which are induced by point configurations in a Bruhat Tits building. In this talk, we use these degenerations to construct certain models of plane curves. Motivated by recent advances towards a padic Narasimhan—Sehsadri theorem, we then use these models to construct families of syzygy bundles which admit strongly semistable reduction. This talk is based on a joint work with Annette Werner.

Algebraic Topology on 31 October 2023 at 16:00
Speaker: Bastiaan Cnossen (University of Regensburg)
Title: Genuine sheaves on differentiable stacks
Abstract: Cohomology theories for equivariant spaces typically only depend on the associated quotient stacks X//G. It would thus be desirable to have a flexible framework for cohomology theories for stacks. In this talk, I will present such a framework, following ideas from motivic homotopy theory. The main result is a version of relative Poincaré duality for differentiable stacks, which generalizes Poincaré duality for smooth manifolds, Atyah duality for equivariant manifolds, and the Wirthmüller isomorphism in equivariant stable homotopy theory.

Analysis on 31 October 2023 at 15:15
Speaker: Or Hershkovits (Hebrew University of Jerusalem)
Title: Hopf Lemma for Brakke Flows
Abstract: In this talk, I will describe a variant of the classical Hopf lemma, that allows to show regularity (and nonvanishing angle) at (boundary) intersection points of two Brakke flows which are disjoint in a half of a parabolic ball.
This Hopf Lemma can be used in the moving plane method, allowing to prove symmetry and regularity in tandem.
This is based on a joint work with Kyeongsu Choi, Robert Haslhofer and Brian White. 
Ergodic Theory and Dynamical Systems on 31 October 2023 at 14:00
Speaker: Francois Ledrappier (Jussieu)
Title: Dimension of limit sets for Anosov representations
Abstract: We consider the action of discrete finitely generated subgroup of matrices on the space of flags. Under hyperbolicity and nondegeneracy conditions, we can estimate the dimension of minimal invariant sets. The proofs use properties of random walks on the group. This is joint work with Pablo Lessa (Montevideo).

Partial Differential Equations and their Applications on 31 October 2023 at 12:00
Speaker: Markus Schmidtschen (TU Dresden)
Title: TBA
Abstract: TBA

Algebra on 30 October 2023 at 17:00
Speaker: Lucia Morotti (University of York)
Title: Selfextensions for irreducible representations of symmetric groups
Abstract: It has been conjectured that irreducible representations of symmetric groups have no nontrivial selfextensions in characteristic different from 2, that is that the only modules V with 2 composition factors isomorphic to D for some irreducible module D and no other composition factor are those of the form D + D. This conjecture has been proved for some classes of modules by KleshchevSheth and KleshchevNakano. I will present joint results with Harry Geranios and Sasha Kleshchev and current work with Harry Geranios considering reduction results and generalisations of the above mentioned papers.

Junior Analysis and Probability Seminar on 30 October 2023 at 15:00
Speaker: Phoebe Valentine (Warwick)
Title: Characterising 1rectifiability via connected tangents
Abstract: A central concept in geometric measure theory is that of rectifiability. A set is called nrectifiable if it can be covered almost everywhere by images of Lipschitz maps and is purely nunrectifiable if its intersection with any rectifiable set has 0 measure. In this talk, we will start by motivating why tangents are a natural lens through which to view rectifiability. Indeed, the theory of Euclidean tangents has been well developed for some time, and in the case of 1rectifiability we will discuss a geometric proof of a well known Euclidean linear approximability result. We will depend heavily on the inherent "gappiness" of purely 1unrectifiable sets, as quantified by Besicovitch in 1938. We will then consider the problems in generalising this argument to hold in arbitrary metric spaces and have a gentle introduction to the theory of metric tangents. Finally, we will see how the construction of Besicovitch may be strengthened to show that the existence of connected metric tangents implies 1rectifiability.

Junior Number Theory on 30 October 2023 at 11:00
Speaker: Maryam Nowroozi (University of Warwick)
Title: Perfect Powers in Elliptic Divisibility Sequences
Abstract: The problem of determining all perfect powers in a sequence has always been interesting to mathematicians. The problem we are interested in is to prove that there are finitely many perfect powers in elliptic divisibility sequences. Abdulmuhsin Alfaraj proved that there are finitely many perfect powers in elliptic divisibility sequences generated by a nonintegral point on elliptic curves of the from y^2=x(x^2+b), where $b$ is any positive integer. The main goal of our project is to generalize this result for elliptic divisibility sequences generated by any nonintegral point on all elliptic curves y^2=x^3+ax^2+bx+c. This is a joint work with Samir Siksek.

Colloquium on 27 October 2023 at 16:00
Speaker: Juergen Branke (Warwick Business School)
Title: Bayesian Optimisation and Common Random Numbers
Abstract: Bayesian optimisation algorithms are global optimisation algorithms for expensivetoevaluate blackbox problems, as they often occur when a solution candidate needs to be evaluated using simulation or physical experiments. They build a surrogate model, usually a Gaussian Process, based on the data collected to far, and then use this surrogate model to decide which new solution candidate to evaluate in the next iteration to maximise the value of information gained.
This makes the algorithm very sample efficient, and in recent years, Bayesian optimisation has become very popular in particular for machine learning hyperparameter tuning and engineering design.
This talk will start with a general introduction to Bayesian optimisation, discussing some of the key open challenges. The second part will then focus on how to effectively exploit common random numbers. Many objective functions (e.g., stochastic simulators) require a random number seed as input. By explicitly reusing a seed, the algorithm can compare two or more solutions under the same randomly generated scenario, such as a common customer stream in a job shop problem, or the same random partition of training data into training and validation set for a machine learning algorithm. Our proposed Knowledge Gradient for Common Random Numbers exploits this and iteratively determines a combination of solution candidate and random seed to evaluate next. 
Combinatorics on 27 October 2023 at 14:00
Speaker: Yani Pehova (LSE)
Title: The ErdősRothschild problem for dichromatic triangles
Abstract: TBA

Mathematics Teaching and Learning on 26 October 2023 at 16:00
Speaker: Helena Verrill (Warwick)
Title: Mathematics games developed by students taking the IATL course on serious tabletop games
Abstract: I will discuss the use of games in teaching mathematics. This is particularly focused on the games developed by students taking the serious tabletop games IATL module (IL031/131). I will bring three of these games to the talk, and talk about how these games are played, and consider how students' learning can be impacted by use of games. I will mention how I have occasionally used games or puzzles in my own teaching.

Statistical Mechanics on 26 October 2023 at 16:00
Speaker: Sabine Bögli (University of Durham)
Title: On the discrete eigenvalues of Schrödinger operators with complex potentials
Abstract: In this talk I shall present constructions of Schrödinger operators with complexvalued potentials whose spectra exhibit interesting properties. One example shows that for sufficiently large p, the discrete eigenvalues need not be bounded in modulus by the $L^p$ norm of the potential. This is a counterexample to the LaptevSafronov conjecture (Comm. Math. Phys. 2009). Another construction proves optimality (in some sense) of generalisations of LiebThirring inequalities to the nonselfadjoint case  thus giving us information about the accumulation rate of thediscrete eigenvalues to the essential spectrum. This talk is based on joint works with JeanClaude Cuenin (Loughborough) and Frantisek Stampach (Prague).

Analysis on 26 October 2023 at 16:00
Speaker: Denis Marti (Freibourg)
Title: Geometric and Analytic Structures on Metric Spaces Homeomorphic to a Manifold
Abstract: We explore geometric and analytic aspects of metric spaces homeomorphic to a closed, oriented manifold. We show that such spaces (which are sometimes called metric manifolds) admit a nontrivial integral current without boundary, provided they satisfy some weak assumptions. The existence of such an object should be thought of as an analytic analogue of the fundamental class of the space and can also be interpreted as giving a way to make sense of Stokes' theorem in this setting. We use this to establish (relative) isoperimetric inequalities in metric nmanifolds that are Ahlfors nregular and linearly locally contractible. As an application, we obtain a short and conceptually simple proof of a deep theorem of Semmes about the validity of Poincaré inequalities in these spaces. We furthermore present applications to the problem of Lipschitzvolume rigidity in the case of metric manifolds. Based on joint work with G. Basso and S. Wenger.

Probability Theory on 25 October 2023 at 16:00
Speaker: Julien Sabin (University of Rennes)
Title: Nonlinear Hartree dynamics for density matrices
Abstract: In this talk I will review results concerning the meanfield dynamics of fermionic quantum particles governed by the nonlinear Hartree equation. The particularity of this equation is that its unknown is a bounded operator on a Hilbert space, rather than a (wave)function as is the case for most PDEs. I will explain how to deal with setting, with a focus on the large time behaviour of solutions.

Algebraic Geometry on 25 October 2023 at 15:00
Speaker: Farhad Babaee (Bristol)
Title: Complex tropical currents
Abstract: In this talk, I will recall basic ideas in tropical geometry and the theory of positive currents, and I will discuss why exploring the interactions of these two domains is natural and useful.

Analysis on 24 October 2023 at 16:00
Speaker: Or Hershkovits (Hebrew University of Jerusalem)
Title: Mean curvature flow in spaces with positive cosmological constant
Abstract: In this talk, I will describe an approach of using Lorentzian mean curvature flow (MCF) to probe cosmologies satisfying the Einstein equation with positive cosmological constant with matter obeying the strong energy condition.
Assuming surface symmetry, I will explain how such flow converges, in some sense, to the standard constant mean curvature (CMC) slicing of de Sitter space, implying in particular, that such cosmologies are themselves asymptotic to de Sitter space.
I will then illustrate a condition, natural in the above context, such that any local graphical mean curvature flow (without symmetry) in de Sitter space satisfying that condition converges to the standard CMC slicing of the entire de Sitter space.
Effort will be made to make the talk accessible to the wide mathematical audience. This is based on a joint work with Creminelli, Senatore and Vasy, and on a joint work with Senatore. 
Algebraic Topology on 24 October 2023 at 16:00
Speaker: Itamar Mor (Queen Mary University of London)
Title: Profinite Galois descent in K(n)local homotopy theory
Abstract: Using condensed mathematics, I give a construction of the K(n)local E_nAdams spectral sequence as a HFPSS for the continuous action of the Morava stabiliser group. A modified version gives a spectral sequence computing the Picard and Brauer groups of K(n)local spectra.

Ergodic Theory and Dynamical Systems on 24 October 2023 at 14:00
Speaker: Irving Calderon (Durham University)
Title: Explicit spectral gap for Schottky subgroups of $\mathrm{SL} (2, \mathbb{Z})$
Abstract: TBA

Partial Differential Equations and their Applications on 24 October 2023 at 12:00
Speaker: Alexandra Holzinger (University of Oxford)
Title: TBA
Abstract: TBA

Algebra on 23 October 2023 at 17:00
Speaker: Veronica Kelsey (University of Manchester)
Title: Nice and Nasty Numerical Invariants
Abstract: For a permutation group G we can define the maximal irredundant base size and the relational complexity, denoted I(G) and RC(G) respectively. Roughly speaking the maximal irredundant base size is the size of the “worst” base for G, and relational complexity is a measure of when a local property extends to a global one.
We begin by defining these numerical invariants and then cover some examples which illustrate the “nice” behaviour of I(G) and the “nasty” behaviour of RC(G). We’ll then skim through the proof of the relational complexity of a family of groups. 
Junior Analysis and Probability Seminar on 23 October 2023 at 15:00
Speaker: Federico Bertacco (Imperial)
Title: Scaling limits of planar maps under the Smith embedding
Abstract: Over the past few decades, there has been significant progress in the study of scaling limits of random planar maps. In this talk, I will provide motivation for this problem and then focus on the scaling limits of (random) planar maps under the Smith embedding. This embedding is described by a tiling of a finite cylinder by rectangles, where each edge of the map corresponds to a rectangle, and each vertex corresponds to a horizontal segment. I will argue that when considering a sequence of finite planar maps embedded in an infinite cylinder and satisfying a suitable invariance principle assumption, the a priori embedding is close to an affine transformation of the Smith embedding at larger scales. By applying this result, I will prove that the Smith embeddings of matedCRT maps with the sphere topology converge to LQG. This is based on joint work with Ewain Gwynne and Scott Sheffield.

Junior Number Theory on 23 October 2023 at 11:00
Speaker: Arshay Sheth (University of Warwick)
Title: The HilbertPolya dream: finding determinant expressions of zeta functions
Abstract: The HilbertPolya dream, which seeks to express the Riemann zeta function as a characteristic polynomial of an operator on a Hilbert space, is one possible approach to prove the Riemann Hypothesis. While this approach has never been successfully carried out, its core principle finding determinant expression of zeta functions has manifested itself in several different areas of number theory in the last century. In this talk, we will attempt to give a panoramic survey of the HilbertPolya dream.

Colloquium on 20 October 2023 at 16:00
Speaker: Colva RoneyDougal (St Andrews)
Title: Counting permutation groups
Abstract: What does a random permutation group look like? This talk will start with a brief survey of how we might go about counting subgroups of the symmetric group S_n, and talk about what is known about "most" subgroups.
To tackle the general problem, it would clearly be helpful to know how many subgroups there are. An elementary argument gives that there are at least 2^{n^2/16} subgroups, and it was conjectured by Pyber in 1993 that up to lower order error terms this is also an upper bound. This talk will present an answer to Pyber's conjecture.
This is joint work with Warwick’s own Gareth Tracey. 
Combinatorics on 20 October 2023 at 14:00
Speaker: António Girão (Oxford)
Title: On induced C4free graphs with high average degree
Abstract: TBA

Analysis on 19 October 2023 at 16:00
Speaker: Andrea Mondino (Oxford)
Title: Lorentzian Ricci bounds and Einstein’s theory of gravity in a non smooth setting: an optimal transport approach
Abstract: Optimal transport tools have been extremely powerful to study Ricci curvature, in particular Ricci lower bounds in the nonsmooth setting of metric measure spaces (which can be been thought as "nonsmooth Riemannian manifolds”).
Since the geometric framework of general relativity is the one of Lorentzian manifolds (or spacetimes), and the Ricci curvature plays a prominent role in Einstein’s theory of gravity, it is natural to expect that optimal transport tools can be useful also in this setting.
The goal of the talk is to introduce the topic and to report on recent progress.
More precisely: After recalling the general setting of Lorentzian prelength spaces (introduced by KunzingerSämann, after KronheimerPenrose), I will discuss some basics of optimal transport theory thereof in order to define "timelike Ricci curvature and dimension bounds” for a possibly nonsmooth Lorentzian space. Some cases of such bounds have remarkable physical interpretations (like the attractive nature of gravity) and can be used to give a characterisation of the Einstein’s equations for a nonsmooth space and to establish new isoperimetrictype inequalities in Lorentzian signature. Based partly on joint work with S. Suhr and partly on joint work with F. Cavalletti. 
Geometry and Topology on 19 October 2023 at 14:00
Speaker: Clément Legrand (LaBRI)
Title: Reconfiguration of squaretiled surfaces
Abstract: A squaretiled surface is a special case of a quadrangulation of a surface, that can be encoded as a pair of permutations in \(S_n \times S_n\) that generates a transitive subgroup of \(S_n\). Squaretiled surfaces can be classified into different strata according to the total angles around their conical singularities. Among other parameters, strata fix the genus and the size of the quadrangulation. Generating a random squaretiled surface in a fixed stratum is a widely open question. We propose a Markov chain approach using "shearing moves": a natural reconfiguration operation preserving the stratum of a squaretiled surface. In a subset of strata, we prove that this Markov chain is irreducible and has diameter \(O(n^2)\), where \(n\) is the number of squares in the quadrangulation.

Probability Theory on 18 October 2023 at 16:00
Speaker: Anna Maltsev (Queen Mary University London)
Title: Bulk Universality for Complex NonHermitian Gaussdivisible Matrices
Abstract: In this talk I will discuss universality of the kpoint correlation function for Gauss divisible nonHermitian matrices. We consider NxN matrices with centred, independent and identically distributed complex entries that have a small Gaussian component. We prove that the bulk correlation functions are universal in the large N limit using Householder transformations, supersymmetry, and Laplace method. Assuming the entries have finite moments and are supported on at least three points, the Gaussian component is removed by the four moment theorem. This is based on joint work with Mohammed Osman.

Algebraic Geometry on 18 October 2023 at 15:00
Speaker: Vaidehee Thatte (KCL)
Title: Understanding the Defect via Ramification Theory
Abstract: Classically, the degree of a finite Galois extension of complete discrete valuation fields equals the product of two invariants measuring the change in the valuation (ramification index) and the change in the residue field (inertia degree). More generally, there is a third factor  the ‘defect’. For example, we can have a degree p extension with trivial extensions of the value group and the residue field. The defect is not yet well understood and remains the main obstruction to several longstanding open problems in positive residue characteristic (e.g., resolution of singularities). The primary reason is, roughly speaking, that the classical strategy of "objects become nicer after finitely many blowups" fails when the defect is nontrivial. We are thrown into an infinite loop.
In this talk, I will discuss how techniques in arithmetic algebraic geometry, number theory, and valuation theory together can help us understand the defect and deal with the obstacles it creates. In particular, I will present a generalization of the classical invariants of ramification theory, a generalization of GabberRamero's work on 'filtered union', and some recent work (joint with K. Kato) on upper ramification filtration in the general case. Any necessary background in these areas will be covered via examples and rough (practical) definitions. 
Algebraic Topology on 17 October 2023 at 16:00
Speaker: Daniel Kasprowski (University of Southampton)
Title: Stable equivalence relations of 4manifolds
Abstract: Kreck’s modified surgery gives an approach to classify 2nmanifolds up to stable diffeomorphism, i.e., up to a connected sum with copies of S^n x S^n. In dimension 4, we use a combination of modified and classical surgery to compare the stable diffeomorphism classification with other stable equivalence relations. Most importantly, we consider homotopy equivalence up to connected sum with copies of S^n x S^n. This is joint work with John Nicholson and Simona Veselá.

Ergodic Theory and Dynamical Systems on 17 October 2023 at 14:00
Speaker: Roberto Castorrini (University of Pisa)
Title: Transfer operators, spectral gap and thermodynamic formalism: from smooth to discontinuous dynamical systems
Abstract: I will provide a brief overview of the functional approach used to analyze the statistical properties of a dynamical system, focusing on its main objective: determining a suitable Banach space that minimizes the 'noncompact' (essential) part of the spectrum of the associated transfer operator. Optimal outcomes regarding the essential spectrum for smooth hyperbolic dynamical systems are attained by employing thermodynamic formalism techniques, which utilize a variational expression for subadditive topological pressure. Drawing from a recent joint work with V. Baladi, I will illustrate similar results for systems with discontinuities, particularly piecewise expanding maps in finite dimensions.

Algebra on 16 October 2023 at 17:00
Speaker: Stacey Law (University of Birmingham)
Title: Sylow branching coefficients for symmetric groups
Abstract: One of the key questions in the representation theory of finite groups is to understand the relationship between the characters of a finite group G and its local subgroups. Sylow branching coefficients describe the restriction of irreducible characters of G to a Sylow subgroup P of G, and have been recently shown to characterise structural properties such as the normality of P in G. In this talk, we will discuss and present some new results on Sylow branching coefficients for symmetric groups.

Junior Analysis and Probability Seminar on 16 October 2023 at 15:00
Speaker: Julian Weigt (Warwick)
Title: Endpoint regularity bounds for maximal operators in higher dimensions
Abstract: The classical HardyLittlewood maximal function theorem states that maximal operators are bounded on L^p(ℝ^n) if and only if p>1. In 1997 Juha Kinnunen proved that for p>1 also the gradient of a maximal function is bounded on L^p(ℝ^n). It is an open question in the endpoint p=1. In one dimension this endpoint gradient bound is known to hold for most maximal operators due to Tanaka, Kurka and many others.
We prove the endpoint gradient bound in all dimensions for the maximal operator that averages over uncentered cubes with any orientation. For the uncentered HardyLittlewood maximal operator we can prove the endpoint Sobolev bound only in the case of characteristic functions since some of our arguments only work for cubes and not for balls. Moreover, we prove the corresponding endpoint Sobolev bound for the fractional centered and uncentered HardyLittlewood maximal functions.
The key arguments are of geometric nature and rely on the coarea formula, the relative isoperimetric inequality and covering lemmas. 
Junior Number Theory on 16 October 2023 at 11:00
Speaker: Isabel (Izzy) Rendell (King's College London)
Title: Rational points on modular curves
Abstract: The problem of finding rational points on modular curves is of great interest in number theory and arithmetic geometry, with many different methods in use in the subject. This will be an introductory talk where will see some key related theorems due to Faltings, Coleman and Mazur. I will discuss some methods for finding rational points, and how they can relate to other areas such as points on elliptic curves and the congruent number problem. Throughout the talk I will try and assume as few prerequisites as possible and demonstrate methods by examples.

Colloquium on 13 October 2023 at 16:00
Speaker: Rob Silversmith (Warwick)
Title: Counting problems in algebraic geometry
Abstract: Choose five conic plane curves randomly. There are exactly 3264 ways to draw a sixth conic that is tangent to all five. (You may need complex numbers to see all of them.) Counting problems like this one have been studied for hundreds of years, and are part of a rich interplay between geometry and combinatorics. I will discuss a very downtoearth class of counting problems with connections to many fields, including: string theory, rigid frameworks, polyhedral geometry, matroid theory, and cluster algebras. I will also mention some other recent developments and directions in the field.

Combinatorics on 13 October 2023 at 14:00
Speaker: Abhishek Methuku (ETH)
Title: The extremal number of cycles with all diagonals
Abstract: TBA

Analysis on 12 October 2023 at 16:00
Speaker: PakYeung Chan (Warwick)
Title: Gap Theorem for Nonnegatively Curved Manifolds
Abstract: In this seminar, we shall discuss some recent results on the gap theorem of nonnegatively curved manifolds with small curvature in an average integral sense, which can be viewed as a Riemannian analog of the optimal gap result by Ni on Kahler manifolds. In dimension 3, we also establish a gap theorem for Ricci nonnegative manifolds with pointwise quadratic curvature decay and fast average integral curvature decay. This talk is based on a joint work with ManChun Lee.

Geometry and Topology on 12 October 2023 at 14:00
Speaker: Mark Pengitore (University of Virginia)
Title: Residual finiteness growth functions of surface groups with respect to characteristic quotients
Abstract: Residual finiteness growth functions of groups have attracted much interest in recent years. These are functions that roughly measure the complexity of the finite quotients needed to separate particular group elements from the identity in terms of word length. In this talk, we study the growth rate of these functions adapted to finite characteristic quotients. One potential application of this result is towards linearity of the mapping class group

Probability Theory on 11 October 2023 at 16:00
Speaker: Ellen Powell (University of Durham)
Title: Characterising the Gaussian free field
Abstract: I will discuss recent approaches to characterising the Gaussian free field in the plane, and in higher dimensions. This is based on joint work with Juhan Aru, Nathanael Berestycki and Gourab Ray.

Algebraic Geometry on 11 October 2023 at 15:00
Speaker: Calla Tschanz (Bath)
Title: Expanded degenerations for Hilbert schemes of points
Abstract: Let X –> C be a projective family of surfaces over a curve with smooth general fibres and simple normal crossing singularity in the special fibre X_0. We construct a good compactification of the moduli space of relative length n zerodimensional subschemes on X\X_0 over C\{0}. In order to produce this compactification we study expansions of the special fibre X_0 together with various GIT stability conditions, generalising the work of GulbrandsenHalleHulek who use GIT to offer an alternative approach to the work of LiWu for Hilbert schemes of points on simple degenerations. We construct stacks which we prove to be equivalent to the underlying stack of some choices of logarithmic Hilbert schemes produced by MaulikRanganathan.

Algebraic Topology on 10 October 2023 at 16:00
Speaker: Özgür Bayındır (City University of London)
Title: Algebraic Ktheory of the twoperiodic first Morava Ktheory
Abstract: Using a root adjunction formalism developed in an earlier work and logarithmic THH, we obtain a simplified computation of the algebraic Ktheory of the complex Ktheory spectrum. Furthermore, our computational methods also provide the algebraic Ktheory of the twoperiodic Morava Ktheory spectrum of height 1.

Ergodic Theory and Dynamical Systems on 10 October 2023 at 14:00
Speaker: Konstantinos Tsinas (University of Crete)
Title: Ergodic averages along primes
Abstract: We study the limiting behavior of multiple ergodic averages along sequences evaluated at primes. Building on the result of Frantzikinakis, Host, and Kra, who established (in the most general setting known) the corresponding convergence theorem in the case that the sequences are integer polynomials, we generalize their result to other sequences of polynomial growth. The most prominent examples in our work are the fractional powers $\lfloor{n^c}\rfloor$, where $c$ is a positive noninteger. We prove that sets of positive density contain arbitrarily long arithmetic progressions with common difference $\lfloor{ p^c} \rfloor$, where $p$ denotes a prime, along with a few more mean convergence theorems and equidistribution results in nilmanifolds. Our methods rely on a recent deep theorem of Matom\"{a}ki, Shao, Tao, and Ter\"{a}v\"{a}inen on the Gowers uniformity of the von Mangoldt function in short intervals, an approximation of our functions with polynomials with good equidistribution properties and a lifting trick that allows someone to pass from ${\mathbb Z}$actions on a probability space to ${\mathbb R}$actions.

Partial Differential Equations and their Applications on 10 October 2023 at 12:00
Speaker: Ivan Moyano (Unv. Nice Sophia Antipolis)
Title: Spectral Uncertainty principle for LaplaceBeltrami and Schroedinger operators
Abstract: TBAIn this talk we review some classical and recent results
relating the uncertainty principles for the Laplacian with the
controllability and stabilisation of some linear PDEs. The uncertainty
principles for the Fourier transforms state that a square integrable
function cannot be both localised in frequency and space without being
zero, and this can be further quantified resulting in unique
continuation inequalities in the phase spaces. Applying these ideas to
the spectrum of the Laplacian on a compact Riemannian manifold, Lebeau
and Robbiano obtained their celebrated result on the exact
controllability of the heat equation in arbitrarily small time. The
relevant quantitative uncertainty principles known as spectral
inequalities in the literature can be adapted to a number of different
operators, including the LaplaceBeltami operator associated to C^1
metrics or some Schödinger operators with longrange potentials, as we
have shown in recent results in collaboration with Gilles Lebeau (Nice)
and Nicolas Burq (Orsay), with a significant relaxation on the
localisation in space. As a consequence, we obtain a number of
corollaries on the decay rate of damped waves with rough dampings, the
simultaneous controllability of heat equations with different boundary
conditions and the controllability of the heat equation with rough
controls. 
Junior Analysis and Probability Seminar on 09 October 2023 at 15:00
Speaker: Lucas Lavoyer (Warwick)
Title: Ricci flow from spaces with edge type conical singularities
Abstract: In this talk, we will construct a solution to Ricci flow coming out of spaces with edge type conical singularities along a closed, embedded curve, under the additional assumption that for each point of the curve, our space is locally modelled on the product of a fixed positively curved cone and a line. We also prove curvature estimates for the solution and, for edge points, we show that the tangent flow at these points is a positively curved expanding gradient Ricci soliton solution crossed with a line.

Number Theory on 09 October 2023 at 11:00
Speaker: Abdul Alfaraj (University of Bath)
Title: On the Finiteness of Perfect Powers in Elliptic Divisibility Sequences
Abstract: TBA

Colloquium on 06 October 2023 at 16:00
Speaker: AnneSophie Kaloghiros (Brunel)
Title: The Calabi problem for Fano 3folds and applications
Abstract: Algebraic varieties are geometric shapes given by polynomial equations. They appear naturally in pure and applied mathematics: from conic sections in geometry, to cubic curves in cryptography, or nonuniform rational basis splines in computeraided graphic design.
To measure distances between points on an algebraic variety, we equip it with a metric  a sophisticated dot product. This then leads to the notion of curvature, and allows us to split algebraic varieties into three basic (universal) types: negatively curved, flat and positively curved varieties. Positively curved varieties are higher dimensional generalisations of a sphere; they are called Fano varieties. Fano varieties appear frequently in applications, because they are often parametrised by rational functions.
For an algebraic variety, the choice of a metric is never unique. One can try to find a special metric with good properties: a “canonical metric". Geometers looked for a suitable condition defining a canonical metric for the first half of the 20th century. In 1957, Calabi proposed that this canonical metric should satisfy both a certain algebraic property (being Kähler) and the Einstein (partial differential) equation. Finding which compact complex manifolds admit such a metric is the object of the Calabi problem, an area of research at the crossroads of algebraic and differential geometry that has been very active for the last decades.
A necessary condition for the existence of such a metric is that the manifold belongs to one of the three basic universal types. Yau and Aubin/Yau confirmed Calabi's prediction and showed that manifolds with negative or flat curvature always admit a KählerEinstein metric in the 1970s. By contrast, the Calabi problem is much more subtle for manifolds
with positive curvature: Fano manifolds may or may not admit a KählerEinstein metric.
Research on the Calabi problem for Fano manifolds culminated in the formulation and proof of the YauTianDonaldson conjecture. This conjecture, now a theorem, states that a Fano manifold admits a KählerEinstein metric precisely when it satisfies a sophisticated algebrogeometric condition called Kpolystability. Surprisingly, the notion of Kpolystability also sheds some light on their moduli theory, that is how they behave in families ( another poorly understood aspect of their geometry).
In this talk, I will present an overview of the Calabi problem, and present its solution in small dimension ( in which we have a classification of deformation families of smooth Fano varieties). I will discuss applications to other areas such as moduli theory. 
Combinatorics on 06 October 2023 at 14:00
Speaker: Michael Savery (University of Oxford)
Title: Chromatic number is not tournamentlocal
Abstract: TBA

Analysis on 05 October 2023 at 16:00
Speaker: Katie Gittins (Durham University)
Title: Heat Content of Polygonal Domains
Abstract: Let D \subset \mathbb{R}^2 be a bounded set with polygonal boundary \partial D. We impose an initial temperature condition on \mathbb{R}^2 \setminus \partial D and can also impose boundary conditions on the edges of \partial D, such as a Dirichlet (cooling) boundary condition.
In such a setting, it is natural to ask: how much heat is left inside D at time t? This quantity is the heat content of D. The smalltime asymptotic expansions for the heat content of D encode information about the geometry of D and \partial D. Our goal is to explore how these expansions depend upon the geometry and on various combinations of initial and boundary conditions.
We first review some of the previously known results for the smalltime asymptotic expansions for the heat content of D with certain initial and boundary conditions. We then present recent results for the case where D is contained in a larger set with polygonal boundary on which a Neumann (insulating) boundary condition is imposed. The latter is based on joint work with Sam Farrington. Timepermitting, we may also discuss some geometric applications of these asymptotic expansions. 
Geometry and Topology on 05 October 2023 at 14:00
Speaker: Raphael Zentner (Durham University)
Title: Rational homology ribbon cobordism is a partial order
Abstract: Last year, Ian Agol has proved that ribbon knot concordance is a partial order on knots, a conjecture that has been open for more than three decades. His proof is beautiful and surprisingly simple. There is an analog notion of ribbon cobordism for closed 3manifolds. We use Agol's method to show that this notion of ribbon cobordism is also a partial order within the class of irreducible 3manifolds. This is joint work with Stefan Friedl and Filip Misev.

Probability Theory on 04 October 2023 at 16:00
Speaker: Tom Klose (University of Warwick)
Title: Large deviations for the Φ^4_3 measure via Stochastic Quantisation
Abstract: The Φ^4_3 measure is one of the easiest nontrivial examples of a Euclidean quantum field theory (EQFT) whose rigorous construction in the 1970's has been one of the celebrated achievements of the Constructive QFT community. In recent years, progress in the field of singular stochastic PDEs, initiated by the theory of regularity structures, has allowed for a new construction of the Φ^4_3 EQFT as the invariant measure of a previously illposed Langevin dynamics – a strategy originally proposed by Parisi and Wu ('81) under the name Stochastic Quantisation. In this talk, I will demonstrate that the same idea also allows to transfer the large deviation principle for the Φ^4_3 dynamics, obtained by Hairer and Weber ('15), to the corresponding EQFT. Our strategy is inspired by earlier works of Sowers ('92) and Cerrai and Röckner ('05) for nonsingular dynamics and potentially also applies to other EQFT measures. This talk is based on joint work with Avi Mayorcas (University of Bath).

Algebraic Geometry on 04 October 2023 at 15:00
Speaker: Charles Favre (École Polytechnique)
Title: bdivisors and dynamical applications
Abstract: bdivisors were introduced by Shokurov in the context of the minimal model program. We shall explain how to develop a positivity theory of these objects that have remarkable applications to algebraic dynamics.

Ergodic Theory and Dynamical Systems on 03 October 2023 at 14:00
Speaker: Yves Benoist (Université ParisSaclay)
Title: Convolution and square on abelian groups
Abstract: The aim of this talk will be to construct functions on a cyclic group of odd order whose ''convolution square'' is proportional to their square. For that, we will have to interpret the cyclic group as a subgroup of an abelian variety with complex multiplication, and to use the modularity properties of their theta functions.

Ergodic Theory and Dynamical Systems on 12 September 2023 at 14:00
Speaker: Anthony Quas (University of Victoria)
Title: Lyapunov exponents and noise
Abstract: TBA

Statistical Mechanics on 16 August 2023 at 14:00
Speaker: Jiwoon Park (Cambridge)
Title: Finitesize scaling of the hierarchical $\phi^4 $  model in dimension 4 and higher
Abstract: The lattice phi4 model is a spin model subject to a quartic potential function. It is believed to be in the same universality class as the O(N) model, and its critical behaviour has been a subject of renormalisation group analysis with small coupling constant assumption for a long time. In dimension 4 or higher, it was observed that the boundary condition plays a crucial role in finitesize scaling at the critical point, but there was a relative lack of work on the principles underlying this phenomenon. In this talk, I will define the hierarchical phi4 model, a toy model for renormalisation group analysis, and show some rigorous results that helps understanding the critical finitesize scaling.
(Joint work with Gordon Slade and Emmanuel Michta) 
Applied Mathematics on 30 June 2023 at 12:00
Speaker: Eric Rogers (Southampton)
Title: Optimizationbased Iterative Learning Control with Applications in Physics, Engineering, and Healthcare
Abstract: Many physical systems complete the same finiteduration task over and over again. One example in robotic applications is the `pick and place’ task, where the mission is to move a sequence of payloads from a fixed location and place them in synchronization on a moving conveyor. The series of operations is as follows: i) collect the payload from the specified location, ii) transfer it over a finite duration, iii) place it on the moving conveyor, iv) return to the starting location, and repeat this sequence for as many payloads as required or until a stop is required for maintenance or other reasons.
Iterative learning control emerged in the mid1980s for application to examples such as the one just described, and since then has been a very active research and applications area. This seminar will first describe the development of an optimizationbased design in a Hilbert space setting and then demonstrate its application, with supporting experimental results, to freeelectron lasers, rack feeders, and roboticassisted stroke rehabilitation. Some currently open research problems will also be briefly discussed. 
2023 LMS Hardy Lecture on 28 June 2023 at 16:00
Speaker: Eva Miranda (Universitat Politècnica de Catalunya)
Title: Euler flows as universal models for dynamical systems
Abstract: The dynamics of an inviscid and incompressible fluid flow on a Riemannian manifold is governed by the Euler equations. In this talk we will discuss universality properties of the stationary solutions to the Euler equations. The study of these universality features was suggested by Tao as a novel way to address the problem of global existence for Euler and NavierStokes. Universality of the Euler equations for stationary solutions can be proved using a contact mirror which reflects a Beltrami flow as a Reeb vector field. This contact mirror permits the use of advanced geometric techniques such as the hprinciple in fluid dynamics.

Algebraic Topology on 27 June 2023 at 16:00
Speaker: Maxime Ramzi (University of Copenhagen)
Title: Separability in homotopical algebra
Abstract: Separable algebras are a generalization of étale algebras that can be defined in more general homotopical contexts, and have been studied in tensortriangular geometry, partly due to their nice properties in this context.
In this talk, I will attempt to explain some of these nice properties in tensortriangulated categories, by showing that they come from surprising features of separable algebras in stable oocategories, in particular showing that all separable uptohomotopy algebras lift (almost) uniquely to homotopy coherent algebras. If time permits, I will also mention how the basics of the classical theory of separable algebras extend to homotopical algebra. 
Number Theory on 26 June 2023 at 15:00
Speaker: Shreyasi Datta (Michigan)
Title: TBA
Abstract: TBA

Colloquium on 23 June 2023 at 16:00
Speaker: Joel Moreira (Warwick)
Title: Ergodic approaches to arithmetic Ramsey theory
Abstract: Ramsey theory is a branch of combinatorics which seeks to find patterns in disorganized situations. One of its main achievements, Szemeredi’s theorem on arithmetic progressions, got an ergodic theoretic proof in 1977 when Furstenberg created a Correspondence Principle to encode combinatorial information about sets of integers into a dynamical system. Since then ergodic methods have been very successful in obtaining new Ramsey theoretic results, some of which still have no purely combinatorial proof.
I will survey some of the history of how ergodic theory and Ramsey theory are interconnected, leading to a recent result involving infinite sumsets. 
Combinatorics on 23 June 2023 at 14:00
Speaker: Marcelo Campos (University of Oxford)
Title: The least singular value of a random symmetric matrix
Abstract: Let $A$ be a random matrix taken uniformly at random from the set of all $n\times n$ symmetric matrices with entries in {1,+1}. Let $s_n(A)$ be the smallest singular value of $A$. In this talk, I will present a result where we show $$P(s_n\leq \eps/\sqrt{n})\leq C\eps +\exp(cn)$$ for fixed constants $C,c>0$ and all $\eps\geq 0$. In particular this implies $$P(\det(A)=0)\leq \exp(cn)\, .$$

Applied Mathematics on 23 June 2023 at 12:00
Speaker: Susanne Horn (Coventry)
Title: The Elbert Range of Turbulent Rotating Magnetoconvection
Abstract: Turbulent rotating magnetoconvection is fundamental to the fluid processes occurring deep inside planets, including the generation of the geodynamo in Earth’s liquid metal core. But planetary interiors are shielded from direct observation, thus, idealised, physicsdriven models are essential for gaining a detailed understanding. The canonical system is RayleighBenard convection, i.e. a fluid layer heated from below and cooled from above, rotated around the vertical axis and subject to an external magnetic field. This system is characterised by rich multimodal flow behaviours. Depending on the control parameters, a mix of boundaryattached, oscillatory, and geostrophic, magnetostrophic, and magnetic stationary modes constitutes the dynamics of the system. In particular, when thermal convection is subject to both a strong magnetic field and rapid rotation, two very distinct stationary modes can coexist: a smallscale geostrophic and a largescale magnetostrophic mode. This is in stark contrast to the monomodal stationary solution if only one of these constraints is present. The original discovery of this peculiar and unique property goes back to Donna DeEtte Elbert [1]. Recently, we expanded on the linear stability work by Elbert and derived novel predictions for the regimes at which the various types of rotating magnetoconvection occur [2]. The geophysically most relevant regime, i.e. where most planetary bodies reside, exhibits the strongest multimodality, and we coined this regime the Elbert range.
In this talk, I will address the question which of Elbert’s different modes exist and, if any, dominate in strongly nonlinear, turbulent laboratory, as well as planetary and astrophysical settings. I will present results from direct numerical simulations (DNS) of turbulent thermal rotating magnetoconvection. Examplary flow fields are shown in figure 1. Specifically, I will discuss which onset characteristics, such as the length scales and flow morphology, carry over to higher supercriticalities. I will focus on the Elbert range and explore if and how magnetostophic convection can create large length scales and thus provide favourable conditions for the dynamo generation in planetary cores.
[1] Chandrasekhar, Hydrodynamic and hydromagnetic stability, Clarendon (1961)
[2] Horn and Aurnou, Proc. R. Soc. A 478, 2264 (2022) 
Analysis on 22 June 2023 at 16:00
Speaker: Albert Wood (National Taiwan University)
Title: CohomogeneityOne Lagrangian Mean Curvature Flow
Abstract: Lagrangian mean curvature flow is the name given to the observation that the class of Lagrangian submanifolds of CalabiYau manifolds is preserved under mean curvature flow. This observation gave rise to a conjecture of ThomasYau, which states that assuming a stability condition on the Lagrangian, the flow should converge to a unique volumeminimising representative. Since mean curvature flow typically forms finitetime singularities, a surgery procedure must be defined to resolve the conjecture, and an understanding of the possible singularity models is a vital first step.
In this work, we study Lagrangians that are invariant with respect to a group action respecting the CalabiYau structure with (n1)dimensional orbits. Such Lagrangians must be contained in an (n+1)dimensional submanifold, a level set of the moment map, and taking the symplectic quotient produces a curve in a 2manifold. Lagrangian mean curvature flow may therefore be studied via a related curve shortening flow, which we show does not depend on the group action. By this method, we are able to classify cohomogeneityone shrinking and expanding solitons, as well as fully classify singularities in the case of the zero level set. 
Probability Theory on 21 June 2023 at 16:00
Speaker: Daniel Kious (University of Bath)
Title: Random walk on the simple symmetric exclusion process
Abstract: In this talk, I will overview works on random walks in dynamical random environments. I will recall a result obtained in collaboration with Hilário and Teixeira and then I will focus on a work with Conchon–Kerjan and Rodriguez. Our main interest is to investigate the longterm behaviour of a random walker evolving on top of the simple symmetric exclusion process (SSEP) at equilibrium, with density ρ ∈ [0, 1] and rate γ > 0. At each jump, the random walker is subject to a drift that depends on whether it is sitting on top of a particle or a hole. The papers we will discuss imply a law of large numbers for the random walker for all densities ρ except at most one value ρ_0, where the speed, seen as a function of the density, possibly jumps to, from or over 0.

Algebraic Topology on 20 June 2023 at 16:00
Speaker: Sil Linskens (University of Bonn)
Title: Globally equivariant topological modular forms
Abstract: An extension of elliptic cohomology theories to a cohomology theory for equivariant spaces has been a dream for many years, ever since the axiomatics for such a theory were laid down by GinzburgKapranovVasserot in 1995. Recently, a rigorous construction of such a theory was suggested by Lurie using the theory of spectral algebraic geometry, and carried out by GepnerMeier. Given an oriented elliptic curve E> M and an abelian compact Lie group G, the result of the construction is an equivariant cohomology theory Ell_G(): Top_G > Sp, which they show is represented by a (genuine) Gspectrum E_G when G is a torus. However there is a more basic object at play. The cohomology theory Ell_G() is in fact given by restricting a functor Ell():Stk —> Sp defined on stacks along the quotient stack construction ()//G:Top_G—>Stk. One may hope that the functor Ell() should itself be a “(genuine) cohomology theory for stacks”. Such theories are represented by global spectra in the sense of Schwede. In this talk I will explain how one can show that the functor Ell() is in fact represented by a global spectrum E_gl, i.e. defines a genuine cohomology theory on stacks. This is joint work with David Gepner and Luca Pol. The construction crucially makes use of an alternative model of global spectra, recently introduced in joint work with Denis Nardin and Luca Pol. I will also introduce this model in the talk.

Number Theory on 19 June 2023 at 15:00
Speaker: ChiYun Hsu (Lille)
Title: TBA
Abstract: TBA

Colloquium on 16 June 2023 at 16:00
Speaker: Gareth Tracey (Warwick)
Title: How many subgroups are there in a finite group?
Abstract: Counting the number of subgroups in a finite group has numerous applications, ranging from enumerating certain classes of finite graphs (up to isomorphism), to counting how many isomorphism classes of finite groups there are of a given order. In this talk, I will discuss the history behind the question; why it is important; and what we currently know.

Applied Mathematics on 16 June 2023 at 12:00
Speaker: Edward Hinton (Melbourne)
Title: Containment of viscous fluid atop a crystal bed, and application to magmatic ore deposits
Abstract: Increasing electrification of transport and energystorage systems across the world is driving rapid growth in the consumption of key metals. Locating highgrade ores of such metals requires a detailed understanding of the physical and geological processes that governed their formation. Within flowing magma, nickel, copper, and platinum group elements are preferentially transferred into the sulphide liquid phase, which eventually forms the valuable ores. Here, we investigate the dynamics of a thin, coalesced volume of sulphiderich liquid atop a poorly consolidated silicate meltcrystal mush. Four stages of the motion are identified with the crystal levees enabling the eventual trapping of a significant fraction of the liquid sulphide.

Analysis on 15 June 2023 at 16:00
Speaker: Alex Mramor (University of Copenhagen)
Title: Some applications of the mean curvature flow to self shrinkers
Abstract: In this talk I’ll discuss some result on self shrinkers in R^3 and R^4 using the mean curvature flow, including some new work on the unknottedness of shrinkers in R^3 with multiple asymptotically conical ends.

Probability Theory on 14 June 2023 at 16:00
Speaker: Willem van Zuijlen (Freie Universität Berlin and WIAS)
Title: Weakly self avoiding walk in a random potential
Abstract: We investigate a model of simplerandom walk paths in a random environment that has two competing features: an attractive one towards the highest values of a random potential, and a selfrepellent one in the spirit of the wellknown weakly selfavoiding random walk. We tune the strength of the second effect such that they both contribute on the same scale as the time variable tends to infinity. In this talk I will discuss our results on the identification of (1) the logarithmic asymptotics of the partition function, and (2) of the path behaviour that gives the overwhelming contribution to the partition function. This is joint work with Wolfgang König, Nicolas Pétrélis and Renato Soares dos Santos.

Number Theory on 12 June 2023 at 15:00
Speaker: Ila Varma (Toronto)
Title: Malle's Conjecture for octic D4fields
Abstract: We consider the family of normal octic fields with Galois group D4, ordered by their discriminant. In joint work with Arul Shankar, we verify the strong Malle conjecture for this family of number fields, obtaining the order of growth as well as the constant of proportionality. In this talk, we will discuss and review the combination of techniques from analytic number theory and geometryofnumbers methods used to prove these results.

Colloquium on 09 June 2023 at 16:00
Speaker: Julia Wolf (Cambridge)
Title: When is a mathematical object wellbehaved?
Abstract: We will come at this question from two different angles: first, from the viewpoint of model theory, a subject in which for nearly half a century the notion of stability has played a central role in describing tame behaviour; secondly, from the perspective of combinatorics, where socalled regularity decompositions have enjoyed a similar level of prominence in a range of finitary settings, with remarkable applications including to patterns in the primes. In recent years, these two fundamental notions have been shown to interact in interesting ways. In particular, it has been shown that mathematical objects that are stable in the modeltheoretic sense admit particularly wellbehaved regularity decompositions. In this talk we will illustrate this fruitful interplay in the context of both finite graphs and subsets of abelian groups.

Applied Mathematics on 09 June 2023 at 12:00
Speaker: Masha Dvoriashyna (Oxford)
Title: Bacterial hydrodynamics: reorientation during tumbles and viscoelastic lift
Abstract: Bacteria represent the major component of the world’s biomass. A number of these bacteria are motile and swim with the use of flagellar filaments, which are slender helical appendages attached to a cell body by a flexible hook. Low Reynolds number hydrodynamics is the key for flagella to generate propulsion at a microscale [1]. In this talk I will discuss two topics related to swimming of a model bacterium Escherichia coli (E. coli).
E. coli has many flagellar filaments that are wrapped in a bundle and rotate in a counterclockwise fashion (if viewed from behind the cell) during the socalled ‘runs’, wherein the cell moves steadily forward. In between runs, the cell undergoes quick ‘tumble’ events, during which at least one flagellum reverses its rotation direction and separates from the bundle, resulting in erratic motion in place. Alternating between runs and tumbles allows cells to sample space by stochastically changing their propulsion direction after each tumble. In the first part of the talk, I will discuss how cells reorient during tumble and the mechanical forces at play and show the predominant role of hydrodynamics in setting the reorientation angle [2].
In the second part, I will talk about hydrodynamics of bacteria near walls in viscoelastic fluids. Flagellar motility next to surfaces in such fluids is crucial for bacterial transport and biofilm formation. In Newtonian fluids, bacteria are known to accumulate near walls where they swim in circles [3,4], while experimental results from our collaborators at the Wu Lab (Chinese University of Hong Kong) show that in polymeric liquids this accumulation is significantly reduced. We use a combination of analytical and numerical models to propose that this reduction is due to a viscoelastic lift directed away from the plane wall induced by flagellar rotation. This viscoelastic lift force weakens hydrodynamic interaction between flagellated swimmers and nearby surfaces, which results in a decrease in surface accumulation for the cells.
References
[1] Lauga, Eric. "Bacterial hydrodynamics." Annual Review of Fluid Mechanics 48 (2016): 105130.
[2] Dvoriashyna, Mariia, and Eric Lauga. "Hydrodynamics and direction change of tumbling bacteria." Plos one 16.7 (2021): e0254551.
[3] Berke, Allison P., et al. "Hydrodynamic attraction of swimming microorganisms by surfaces." Physical Review Letters 101.3 (2008): 038102.
[4] Lauga, Eric, et al. "Swimming in circles: motion of bacteria near solid boundaries." Biophysical journal 90.2 (2006): 400412. 
Analysis on 08 June 2023 at 16:00
Speaker: Julian Weigt (University of Warwick)
Title: A weighted fractional Poincaré inequality
Abstract: The celebrated fractional Poincaré inequality by BourgainBrezisMironescu bounds the oscillation of a function by an integral over finite differences.
We prove a weighted generalization where we bound the oscillation of a function against a Radon measure by an integral over finite differences against the fractional maximal function of that measure.
This also yields an improvement of the classical MeyersZiemer theorem in several ways.
The proof is based on a fractional isoperimetric inequality and is new even in the nonweighted setting.
We also extend the celebrated PoincaréSobolev estimate with A_p weights of FabesKenigSerapioni by means of a fractional type result in the spirit of BourgainBrezisMironescu.
In contrast to the classical result by BourgainBrezisMironescu, L^pversions of the weighted Poincaré inequality do not hold for p>1 and we provide counterexamples which attest to that in most cases. 
Algebraic Geometry on 07 June 2023 at 15:00
Speaker: Nicola Pagani (Liverpool)
Title: A wallcrossing formula for universal BrillNoether classes
Abstract: We will discuss an explicit graph formula, in terms of boundary strata classes, for the wallcrossing of universal (=over the moduli space of stable curves) BrillNoether classes. More precisely, fix two stability conditions for universal compactified Jacobians that are on different sides of a wall in the stability space. Then we can compare the two universal BrillNoether classes on the two compactified Jacobians by pulling one of them back along the (rational) identity map. The calculation involves constructing a resolution by means of subsequent blowups. If time permits, we will discuss the significance of our formula and potential applications. This is joint with Alex Abreu.

Colloquium on 02 June 2023 at 16:00
Speaker: James Maynard (Oxford)
Title: Primes and patterns of zeros of the Riemann zeta function
Abstract: The Riemann Hypothesis is one of the most famous open problems in mathematics, and if proven it would have amazing consequences for our understanding of prime numbers. It turns out many of these applications to primes would still be true even if the Riemann Hypothesis was false, provided counterexamples to the Riemann Hypothesis are suitably ‘rare’. I’ll give an accessible talk about this and some recent work showing how ‘patterns’ of zeros are related to our understanding of primes.

Applied Mathematics on 02 June 2023 at 12:30
Speaker: Ioana Bouros (Warwick)
Title: WarwickLancaster global COVID19 model
Abstract: As the world recovers from the acute phase of the Covid19 pandemic, a key issue is how to avert future large waves of hospitalisations and deaths driven by novel SARSCoV2 variants. Vaccination booster campaigns play an important role in maintaining the level of immunity in the population and reducing the risk of severe outcomes in infected individuals.
In this talk, we present research commissioned by the WHO SAGE Covid19 Working Group. We consider a wave of infections caused by a novel SARSCoV2 variant, and investigate the effects of deploying booster vaccines according to six different agebased prioritisation strategies. We use eight different exemplar countries from around the world as test cases, chosen to cover a range of socioeconomic backgrounds. The aim is to identify which vaccine targeting strategies are most beneficial in terms of reducing infection and severe outcomes of infection, given a limited number of available booster vaccines.
This work extends earlier research conducted when the level of both infection and vaccinationderived immunity was lower than it is now. In all countries considered, we show that prioritising the eldest and most vulnerable individuals for booster vaccination first is expected to lead to the best public health outcomes (e.g. fewest deaths). Assuming sufficient vaccine supply, serologyinformed booster vaccination strategies are predicted to be of limited benefit compared to simply vaccinating the most vulnerable individuals in the population. We hope that this research is useful for guiding booster vaccination strategies in countries worldwide. 
Applied Mathematics on 02 June 2023 at 12:00
Speaker: Jingbang Liu (Warwick)
Title: Modelling rare rupture of nanoscale liquid thin films
Abstract: Controlling the spontaneous rupture of nanoscale liquid thin films plays a crucial role in various applications such as thinfilm solar cell manufacturing, insulation layer coating, and in labonachip devices. Over the past few decades, theoretical work based on the longwave theory of thin liquid films has successfully identified a critical film height, below which the surface nanowaves become linearly unstable, leading to spontaneous rupture. This dewetting in the socalled ‘spinodal regime’ has been repeatedly confirmed in experiments using atomic force microscopy on polymer films. However, rupture events are also observed for films thicker than the critical film height, which are considered linearly stable, in a different manner. It is believed that the random (Brownian) movement of particles is the cause of dewetting in this ‘thermal regime’ but the theoretical framework predicting the rupture is missing.
In this talk, we present a theory to account for the rupture of a two dimensional linearly stable thin film by utilizing fluctuating hydrodynamics and rare events theory. By modelling the film dynamics with the stochastic thinfilm equation (STF) and solving it numerically, we observe rupture in the linearly stable thermal regime and record the average waiting time for rupture. We show that the STF can be rearranged into the form of a gradient flow, which allows us to apply Kramer’s law from the rare events theory to obtain a theoretical prediction of the average waiting time. Molecular dynamics (MD) simulations are also performed and we find good agreements between the numerics, the prediction, and the MD. As the average waiting time increases exponentially with the thickness of the film, adaptive multilevel splitting method is used in the simulations. 
Analysis on 01 June 2023 at 16:00
Speaker: Ilyas Khan (University of Oxford)
Title: Uniqueness of Asymptotically Conical Gradient Shrinking Solitons in G_2Laplacian Flow
Abstract: Riemannian 7manifolds with holonomy equal to the exceptional Lie group G_2 are intensely studied objects in diverse domains of mathematics and physics. One approach to understanding such manifolds is through natural flows of 3forms called G_2structures, the most prominent of which is Bryant’s Laplacian flow. In general, Laplacian flow is expected to encounter finitetime singularities and, as in the case of other flows, selfsimilar solutions should play a major role in the analysis of these singularities. In this talk, we will discuss recent joint work with M. Haskins and A. Payne in which we prove the uniqueness of asymptotically conical gradient shrinking solitons of the Laplacian flow of closed G_2 structures. We will particularly emphasize the unique difficulties that arise in the setting of Laplacian flow (in contrast to the Ricci flow, where an analogous result due to Kotschwar and Wang is wellknown) and how to overcome these difficulties.

Algebraic Geometry on 31 May 2023 at 15:00
Speaker: Milena Hering (University of Edinburgh)
Title: Stability of Toric Tangent bundles
Abstract: In this talk I will give a brief introduction to slope stability and present a combinatorial criterion for the tangent bundle on a polarised toric variety to be stable in terms of the lattice polytope corresponding to the polarisation. I will then present a theorem that on toric surfaces and toric varieties of Picard rank 2 there exists an ample line bundle such that the tangent bundle is stable if and only if the underlying variety is an iterated blow up of projective space. This is joint work with Benjamin Nill and Hendrik Süss

Number Theory on 30 May 2023 at 15:00
Speaker: Marta Benozzo (LSGNT)
Title: TBA
Abstract: TBA

Combinatorics on 26 May 2023 at 14:00
Speaker: Thomas Karam (University of Oxford)
Title: The structure of the set of minimallength slice rank decompositions of a tensor over a finite field
Abstract: If $k$ is a nonnegative integer and $\mathbb{F}$ is a field, then all length$k$ decompositions of a matrix with rank $k$ over $\mathbb{F}$ can be obtained from one another after a change of basis. In particular, if the field $\mathbb{F}$ is finite, then the number of such decompositions can be expressed in terms of $k$ and $\mathbb{F}$, and is bounded above by $\mathbb{F}^{k^2}$. More generally, if $d \ge 2$ is an integer, then the number of length$k$ tensor rank decompositions of an order$d$ tensor with tensor rank $k$ is bounded above by $\mathbb{F}^{(d1)k^2}$. We will explain how an analogous statement can be obtained for the slice rank: although it is no longer true that the number of length$k$ slice rank decompositions of an order$d$ tensor with slice rank $k$ is bounded above in terms of $d$,$k$ and $\mathbb{F}$, this is nonetheless the case up to a class of transformations which can be described in a simple way.

Applied Mathematics on 26 May 2023 at 12:00
Speaker: Thomas Barker (Cardiff)
Title: Continuum modelling of granular flow with dynamic compressibility
Abstract: Granular flows exhibit a strong dependence on the solids volume fraction in addition to the deformation rate. In the steady inertial regime these dependencies lead to the μ(I),Φ(I)rheology. Here I first show how this model captures key features of the steady flow of grains in vertical pipes  despite this being a complex inhomogenous flow crossing regimes. I then highlight the major shortcoming of the IPhi paradigm: illposedness in transient flow at high packing fractions. Thankfully, this obstacle may be overcome by including the correct dependence on the rate of compression/dilation, which is only nonzero for transient flows.

Analysis on 25 May 2023 at 16:00
Speaker: Klaus Kroncke (KTH Stockholm)
Title: $L^p$stability and positive scalar curvature rigidity of Ricciflat ALE manifolds
Abstract: We prove stability of integrable ALE manifolds with a parallel spinor under Ricci flow, given an initial metric which is close in $L^p\cap L^{\infty}$, for any $p\in (1,n)$, where n is the dimension of the manifold. In particular, our result applies to all known examples of 4dimensional gravitational instantons.
The result is obtained by a fixed point argument, based on novel estimates for the heat kernel of the Lichnerowicz Laplacian. It allows us to give a precise description of the convergence behaviour of the Ricci flow. Our decay rates are strong enough to prove positive scalar curvature rigidity in $L^p$, for each $p\in [1,\frac{n}{n2})$, generalizing a result by Appleton. This is joint work with Oliver Lindblad Petersen. 
Number Theory on 22 May 2023 at 15:00
Speaker: Ian Petrow (UCL)
Title: A nonarchimedean Petersson/Kuznetsov formula, the spectral large sieve, and subconvexity
Abstract: The Petersson/Kuznetsov formula is a spectral summation device for classical automorphic forms that allows one to select forms according to the irreducible admissible unitary representation of GL2(ℝ) that they generate. We present a generalized Petersson/Kuznetsov formula where one may select automorphic forms according to the irreducible admissible unitary representation of GL2(ℚp) that they generate instead. In the case where one selects a single supercuspidal representation of PGL2(ℚp) with even conductor exponent (or, a pair of supercuspidal representations with odd conductor exponent) we present an elegant expression for corresponding Kloosterman sum. As applications, we present a spectral large sieve inequality for these families of automorphic forms, and also applications to cubic moments and subconvexity. Everything in this talk is joint work in progress with M.P. Young and Y. Hu.

Combinatorics on 19 May 2023 at 14:00
Speaker: Jun Yan (University of Warwick)
Title: Distribution of colours in rainbow Hfree colourings
Abstract: An edge colouring of K_n using k colours is said to have colour distribution sequence (e_1,…,e_k) if there are exactly e_i edges of colour i for every i. For every connected graph H, let g(H,k) be the smallest n such that any colour distribution sequence can be realised in a rainbow Hfree colouring of K_n. In 2019, Gyárfás et al proved that g(K_3,k) is finite and posed the question of determining its exact order of magnitude. In the first part of this talk, we resolve this question. In the second part of the talk, which is ongoing joint work with Zhuo Wu, we explore the same question for general H and determine the order of magnitude of g(H,k) except in the case when H has degeneracy 2.

Applied Mathematics on 19 May 2023 at 12:00
Speaker: Rachel Bennett (Bristol)
Title: Coordinating on a surface
Abstract: I will talk about two examples of coordination of active individuals on a surface.
1. On surfaces with many cilia, individual cilia coordinate their beat cycles in the form of metachronal waves. The coordinated beating facilitates selfpropulsion of ciliated microorganisms and creates efficient fluid flow, which is important in several human organs. Here, we consider the connection between single cilium characteristics and the collective behaviour. A theoretical framework is presented using an array of model cilia coordinated by hydrodynamic interactions. We calculate the dispersion relation for metachronal waves and perform a linear stability analysis to identify stable waves. This framework shows how the wave vector, frequency and stability depend on the geometric properties of cilia in the array and the beat pattern of an individual cilium. These results show how information about individual cilia can be used to predict the collective behaviour of many cilia.
2. When Pseudomonas aeruginosa colonises a surface, different colonisation dynamics are observed depending on the attachment mechanism. We investigate two different strategies of two different species. In one strategy, the attachment mechanism of a bacterium helps its neighbours, and in the other strategy the attachment mechanism of an individual helps its progeny. Surprisingly, we find that temporary attachments followed by detachment plays a role in faster colonisation at later times. We study how detachment and division rates affect the overall colonisation dynamics. 
AGATA on 18 May 2023 at 17:00
Speaker: Rhiannon Savage (Oxford)
Title: Derived Geometry Relative to Monoidal Quasiabelian Categories
Abstract: In the theory of relative algebraic geometry, we work with respect to a symmetric monoidal category C. The affines are now objects in the opposite category of commutative algebra objects in C. The derived setting is obtained by working with a symmetric monoidal model or infinitycategory C, with derived algebraic geometry corresponding to the case when we take C to be the category of simplicial modules over a simplicial commutative ring k. Kremnizer et al. propose that derived analytic geometry can be recovered when we instead use complete bornological rings. We can provide an overarching theory by working with commutative algebra objects in certain quasiabelian categories. In this talk, I will introduce these ideas and briefly discuss how we can obtain interesting results, such as a representability theorem for derived stacks in this context.

Analysis on 18 May 2023 at 16:00
Speaker: Alex Waldron (University of Wisconsin  Madison)
Title: Strict typeII blowup in harmonic map flow
Abstract: Finitetime singularities are common in 2D harmonic map flow and very illbehaved in general. However, Topping conjectured that for realanalytic target manifolds, the body map at a singular time will have only removable discontinuities. I'll discuss recent work related to this conjecture: we prove continuity of the body map when the target is CP^n and only (anti)holomorphic bubbles appear, or under the assumption that the blowup is "strictly typeII." Time permitting, I'll also discuss current avenues.

Algebraic Geometry on 17 May 2023 at 15:00
Speaker: Andrew Kresch (University of Zurich)
Title: On rationality in families and equivariant birational geometry
Abstract: In this talk I will recall some developments, connected with rationality in families of varieties, and explain some analogous developments in equivariant birational geometry, obtained in recent joint work with Brendan Hassett and Yuri Tschinkel.

Number Theory on 15 May 2023 at 15:00
Speaker: Caleb Springer (UCL)
Title: Abelian varieties over finite fields and their groups of rational points
Abstract: Abelian varieties are a generalization of elliptic curves, in the sense that they are smooth projective varieties whose rational points form an abelian group. In this talk, we will introduce and deploy algebraic machinery to describe phenomena for the groups of rational points of abelian varieties over finite fields. This machinery can be used to answer many questions. For example, building on work of Howe and Kedlaya, we show that every finite abelian group arises as the group of rational points of some (ordinary) abelian variety defined over the finite field with 2 elements. This is joint work with Stefano Marseglia.

Colloquium on 12 May 2023 at 16:00
Speaker: Frances Kirwan (Oxford)
Title: 2quivers and their representations
Abstract: The theory of quiver representations plays an important role in algebraic geometry and in geometric representation theory. The aim of this talk is to describe some of this theory and to give a glimpse of an extension to 'higher quivers' (which are, very roughly speaking, to quivers as higher categories are to categories), concentrating on 2quivers.

Applied Mathematics on 12 May 2023 at 12:00
Speaker: Luis Espath (Nottingham)
Title: A continuum framework for phase field with bulksurface dynamics
Abstract: This continuum mechanical theory aims at detailing the underlying rational mechanics of bulksurface systems undergoing a phase transition. As a byproduct, we generalize these theories. These types of dynamic boundary conditions are described by the coupling between the bulk and surface partial differential equations for phase fields. Our point of departure within this continuum framework is the principle of virtual powers postulated on an arbitrary part where the boundary may lose smoothness. That is, the normal field may be discontinuous along an edge. However, the edges characterizing the discontinuity of the normal field are considered smooth. Our results may be summarized as follows. We provide a generalized version of the principle of virtual powers for the bulksurface coupling along with a generalized version of the partwise freeenergy imbalance. Next, we derive the explicit form of the surface and edge microtractions along with the field equations for the bulk and surface phase fields. The final set of field equations somewhat resembles the Cahn–Hilliard equation for both the bulk and surface. Moreover, we provide a suitable set of constitutive relations and thermodynamically consistent boundary conditions. We endow the bulksurface system with two types of Robin boundary conditions. Lastly, we derive the Lyapunovdecay relations for these mixed types of boundary conditions for both the microstructure and chemical potential.
Espath, L., 2023. A continuum framework for phase field with bulksurface dynamics. Partial Differential Equations and Applications, 4(1), p.1. 
Analysis on 11 May 2023 at 16:00
Speaker: Anna Siffert (Munster)
Title: Infinitely many pharmonic selfmaps of spheres
Abstract: We study rotationally pharmonic selfmaps between spheres. We prove that for p ∈ N given, there exist infinitely many pharmonic selfmaps of S^m for each m ∈ N with p < m < 2 + p + 2√p. This is joint work with Volker Branding.

Statistical Mechanics on 11 May 2023 at 14:00
Speaker: JeanBernard Bru (Departamento de Matemáticas Facultad de Ciencia y Tecnología Universidad del País Vasco Apartado 644, 48080 Bilbao, Spain BCAM  Basque Center for Applied Mathematics Mazarredo, 14. 48009 Bilbao, Spain)
Title: From ShortRange to MeanField Models in Lattice Quantum Systems
Abstract: Realistic interparticle interactions of quantum manybody systems are largely seen as shortrange. By contrast, meanfield models come from different approximations or Ansätze but are technically advantageous, by allowing explicit computations while capturing surprisingly well many physical phenomena. We will establish a precise mathematical relation between meanfield and shortrange models, by using the longrange limit that is known in the literature as the Kac limit. This paves the way for studying phase transitions, or at least important fingerprints of them like strong correlations at long distances, for models having interactions whose ranges are finite, but very large. It also sheds a new light on meanfield models.

Number Theory on 09 May 2023 at 15:00
Speaker: Rustam Steingart (Heidelberg)
Title: Analytic Cohomology of Lubin–Tate (φ,Γ) Modules
Abstract: If L is a nontrivial finite extension of ℚp there exist Llinear representations of the absolute Galois group GL which are not overconvergent. A sufficient condition to ensure overconvergence is Lanalyticity. This makes it interesting to study analytic extensions of such modules or, more generally, analytic cohomology. Using padic Fourier theory we can, after passing to a large field extension of L, describe these cohomology groups in terms of an explicit "Herrcomplex" which allows us to deduce finiteness and base change properties analogous to the results of Kedlaya–Pottharst–Xiao on continuous cohomology. We also obtain a variant of Shapiro's Lemma for Iwasawacohomology in certain cases. The above results form the technical foundations for studying an "analytic" variant of the local epsilonisomorphism conjecture.

Applied Mathematics on 05 May 2023 at 12:00
Speaker: Hanne Kekkonen (TU Delft)
Title: Random Tree Besov Priors
Abstract: Gaussian process priors are often used in practice due to their fast computational properties. The smoothness of the resulting estimates, however, is not well suited for modelling functions with sharp changes. We propose a new prior that has same kind of good edgepreserving properties than total variation or MumfordShah but correspond to a welldefined infinite dimensional random variable. This is done by introducing a new random variable T that takes values in the space of ‘trees’, and which is chosen so that the realisations have jumps only on a small set.

Analysis on 04 May 2023 at 16:00
Speaker: Teri Soultanis (Warwick)
Title: Curve fragmentwise differentiation of Lipschitz functions on metric spaces
Abstract: Curve fragments are (bi)Lipschitz images of compact subsets of R. They have a surprising connection to differentiability of Lipschitz functions on metric measure spaces, in terms of Alberti representations  decompositions of the measure into curve fragments. In this talk I describe the duality between Alberti representations and modulus (a central tool in Sobolev analysis on metric spaces), the arising curve fragmentwise differentiable structure, and its connection with Lipschitz differentiability spaces.

Algebraic Geometry on 03 May 2023 at 15:00
Speaker: Miles Reid (Warwick)
Title: Cayley cubics and Enriques sextics
Abstract: A Cayley cubic is a cubic surface of PP^3 with nodes at the 4 coordinate points. It automatically passes through the 6 coordinate lines. An Enriques sextic is a sextic surface that passes doubly through the 6 coordinate lines. Putting both of these linear systems together into a graded ring gives a toric extraction of the 6 coordinate lines.
This construction leads naturally to the EnriquesFano variety that is the toric variety (PP^1 x PP^1 x PP^1)/(±1) embedded in PP^13 by monomials corresponding to the facecentred cube. It can also be seen as the midpoint of the standard monoidal transformation PP^3  > PP^3 given by (x,y,z,t) > (1/x,1/y,1/z,1/t). 
Colloquium on 28 April 2023 at 16:00
Speaker: Holly Krieger (Cambridge)
Title: A transcendental dynamical degree
Abstract: In the study of a discrete dynamical system defined by polynomials, we hope as a starting point to understand the growth of the degrees of the iterates of the map. This growth is measured by the dynamical degree, an invariant which controls the topological, arithmetic, and algebraic complexity of the system. I will discuss the history of this question and the recent surprising construction, joint with Bell, Diller, and Jonsson, of a transcendental dynamical degree for an invertible map of this type, and how our work fits into the general phenomenon of power series taking transcendental values at algebraic inputs.

Combinatorics on 28 April 2023 at 14:00
Speaker: Simón Piga (University of Birmingham)
Title: Turán problems in hypergraphs with quasirandom links
Abstract: In this talk, we study Turán problems in quasirandom hypergraphs. In particular, we show that 3uniform hypergraphs with the property that all vertices have a quasirandom link graph with density bigger than 1/3 contain a clique on five vertices. This result is asymptotically best possible.

Applied Mathematics on 28 April 2023 at 12:00
Speaker: Abdessamad Belfakir (Nottingham)
Title: Estimating and Predicting Dynamics of Quantum Systems Using Probability Distribution Function and Klauder Coherent States
Abstract: In this talk, we present an alternative method for estimating and predicting the dynamics of quantum systems through the estimation of the probability distribution function that describes the associated density operator in the Liouvillevon Neumann equation. We demonstrate the effectiveness of this approach by comparing exact and estimated solutions for a Morse oscillator interacting with an external electric field.
The second part of the talk will focus on a generalized su(2) algebra that perfectly describes the discrete energy part of the Morse potential. We also demonstrate the construction of the Klauder coherent state for Morse potential, which satisfies the resolution of identity with a positive measure obtained through the solution of the truncated Stieltjes moment problem. Finally, the time evolution of the uncertainty relation of the constructed coherent states will be analysed. 
Analysis on 27 April 2023 at 16:00
Speaker: Salvatore Stuvard (Milan)
Title: Existence and regularity of Brakke flows: new advances and open questions
Abstract: The Brakke flow is a measuretheoretic generalization of the Mean Curvature Flow which allows to describe the evolution by mean curvature of surfaces admitting singularities and topology changes. A typical example is that of "grain boundaries": the interfaces separating different grains or phases in a material (e.g. a polycrystal) and evolving in time subject to a potential energy of surface tension type.
In this talk, I will discuss some recent advances in the theory concerning existence, qualitative properties, and regularity of Brakke flows, and, if time permits, some applications to Plateau’s problem and the regularity theory for minimal surfaces.
Based on joint works with Yoshihiro Tonegawa (Tokyo Inst. of Tech.). 
Number Theory on 24 April 2023 at 15:00
Speaker: Oren Becker (Cambridge)
Title: Character varieties of random groups
Abstract: The space Hom(\Gamma,G) of homomorphisms from a finitely generated group \Gamma to a complex semisimple algebraic group G is known as the Grepresentation variety of \Gamma. We study this space when G is fixed and \Gamma is a random group in the fewrelators model. That is, \Gamma is generated by k elements subject to r random relations of length L, where k and r are fixed and L tends to infinity.
More precisely, we study the subvariety Z of Hom(\Gamma,G), consisting of all homomorphisms whose images are Zariski dense in G. We give an explicit formula for the dimension of Z, valid with probability tending to 1, and study the Galois action on its geometric components. In particular, we show that in the case of deficiency 1 (i.e., kr=1), the Zariskidense Grepresentations of a typical \Gamma enjoy Galois rigidity.
Our methods assume the Generalized Riemann Hypothesis and exploit mixing of random walks and spectral gap estimates on finite groups.
Based on joint work with E. Breuillard and P. Varju. 
Ergodic Theory and Dynamical Systems on 04 April 2023 at 14:00
Speaker: Anders Öberg (Uppsala University)
Title: Döeblin measures and continuous eigenfunctions of the transfer operator
Abstract: TBA

LMS regional meeting on 27 March 2023 at 14:45
Speaker: Mark Pollicott (Warwick)
Title: Counting geodesic arcs on surfaces with no conjugate points
Abstract: In this talk I will survey classical results of Huber and Margulis on counting geodesic arcs on closed surfaces M of negative curvature. More precisely, there exists h > 0 such that given a point x in M there exists C > 0 such that the number of geodesic arcs starting and ending at x and of length at most T is asymptotic to C exp(h T) as T tends to infinity. I will also discuss the generalization of this result to surfaces with no conjugate points.

Colloquium on 17 March 2023 at 16:00
Speaker: Catherine Powell (Manchester)
Title: The How and Why of Being Intrusive
Abstract: In engineering applications (heat transfer, fluid flow, elasticity etc), we often encounter physicsbased models consisting of partial differential equations (PDEs) with uncertain inputs, which are reformulated as socalled parametric PDEs. Given a probability distribution for the inputs, the forward UQ problem consists of trying to estimate statistical quantities of interest related to the model solution. Conversely, given (usually, noisy) data relating to the model solution, the inverse UQ problem consists of trying to infer the uncertain inputs themselves.
Over the last two decades a myriad of numerical schemes have been developed to tackle the forward and inverse UQ problems for PDE models. The vast majority of these are sampling schemes and are nonintrusive in the sense that users do not have to modify existing solvers and codes for the associated deterministic PDEs. This is very attractive in industrial settings. Stochastic Galerkin methods, also known as intrusive polynomial chaos methods, standard apart and are much less widely used in practise. In this talk, I will outline the intrusive approach, its advantages and limitations, and explain why, if properly implemented, it sometimes offers advantages over sampling methods. 
Combinatorics on 17 March 2023 at 14:00
Speaker: Joseph Hyde (UVic)
Title: Turan Colourings in OffDiagonal Ramsey Multiplicity
Abstract: The Ramsey multiplicity problem asks for the minimum asymptotic density of monochromatic labelled copies of a graph $H$ in a red/blue colouring of $K_n$. As with explicitly calculating Ramsey numbers, this problem is notoriously difficult, with it being solved for only a handful of graphs $H$. Here, and in an accompanying paper ('OffDiagonal Ramsey Multiplicity' by Jonathan Noel and Elena Moss), we introduce an offdiagonal generalization in which the goal is to minimize a certain naturally weighted sum of the densities of red copies of one graph and blue copies of another.
In this talk we will focus on when colourings based on the Tur\'{a}ngraph appear as such minimizers, in particular proving a result based on a recent breakthrough of Fox and Wigderson, who answered the Ramsey multiplicity problem for a certain class of uncommon graphs. Joint work with Jonathan Noel and Jaebaek Lee. 
AGATA on 16 March 2023 at 17:00
Speaker: Javier Aguilar Martin (Univeristy of Kent)
Title: Introduction to derived Ainfinityalgebras
Abstract: We introduce the notion of homotopy associative (Ainfinity) algebras in the framework of operads, with loop spaces as our main example. We will motivate the study of these algebraic structures through the theory of minimal models. We will also see their interaction with brace algebras coming from operadic structures. Derived Ainfinityalgebras will be introduced to overcome the limitations of classical Ainfinityalgebras.

Analysis on 16 March 2023 at 16:00
Speaker: Franz Gmeineder (Konstanz)
Title: Quasiconvexity, (p,q) growth and partial regularity
Abstract: 

Probability Theory on 15 March 2023 at 16:00
Speaker: Neil O'Connell (University College Dublin)
Title: A (Todally cool) Markov chain on reverse plane partitions
Abstract: Abstract: I will discuss a natural Markov chain on reverse plane partitions which is closely related to the Toda lattice and has some remarkable properties. This talk is based on the paper https://arxiv.org/abs/2211.05718 and aimed at a general probability audience. (The fun part of the title is borrowed from `Todally cool stuff’, an informal and very accessible introduction to the Toda lattice, by Barbara Shipman, available at https://faculty.tcu.edu/richardson/seminars/barbaratoda.pdf.)

Algebraic Topology on 14 March 2023 at 16:00
Speaker: Jeffrey Carlson (Imperial College)
Title: Products on Tor and strong homotopy commutativity
Abstract: The Eilenberg–Moore spectral sequence converges from the classical Tor of a span of cohomology rings to the differential Tor of a span of cochain algebras (which is the cohomology of the homotopy pullback). These are both rings, for very different reasons: the first structure comes about because cohomology rings are commutative, and the second arises as a corollary of the Eilenberg—Zilber theorem.
One might well ask when a more general differential Tor of DGAs admits a ring structure, though apparently no one did. We will show that when the DGAs in question admit a certain sort of $E_3$algebra structure generalizing the previous examples, Tor is a commutative graded algebra.
We have not done this out of an innocent interest in homotopycommutative algebras. In the 1960s and '70s there was a flurry of activity developing Ainfinityalgebraic techniques with an aim toward computing the Eilenberg–Moore spectral sequence (for example, of a loop space or homogeneous space). Arguably the most powerful result this program produced was the 1974 theorem of Munkholm that the sequence collapses when the three input spaces have polynomial cohomology over a given principal ideal domain, which however only gives the story on cohomology groups. Our result shows that Munkholm's map is in fact an isomorphism of rings.
This work is joint with several large commutative diagrams. 
Analysis on 14 March 2023 at 15:00
Speaker: Gustav Holzegel (Münster)
Title: Quasilinear wave equations on black hole backgrounds
Abstract: 

Algebra on 13 March 2023 at 17:00
Speaker: Vanthana Ganeshalingam (University of Warwick)
Title: Subgroup Structure of Reductive Groups
Abstract: This talk will introduce the concept of G completereducibility (G cr) originally thought of by Serre in the 90s. This idea has important connections to the open problem of classifying the subgroups of a reductive group G. I will explain the methodology of the classification so far and the main obstacle which is understanding the nonGcr subgroups.

Number Theory on 13 March 2023 at 15:00
Speaker: Cecile Dartyge (Lorraine)
Title: On the largest prime factor of quartic polynomial values : the cyclic and dihedral cases.
Abstract: Let $P(X)$ be an irreducible, monic, quartic polynomial with integral coefficients and with cyclic or dihedral Galois group.
There exists c_P >0 such that for a positive proportion of integers n, P(n) has a prime factor bigger than n^{1+c_p}.
This is a joint work with James Maynard. 
Colloquium on 10 March 2023 at 16:00
Speaker: Matej Balog (DeepMind London)
Title: Discovering faster matrix multiplication algorithms with reinforcement learning
Abstract: Improving the efficiency of algorithms for fundamental computational tasks such as matrix multiplication can have widespread impact, as it affects the overall speed of a large amount of computations. Automatic discovery of algorithms using machine learning offers the prospect of reaching beyond human intuition and outperforming the current best humandesigned algorithms. In this talk I’ll present AlphaTensor, our learned agent for discovering efficient and provably correct algorithms for the multiplication of arbitrary matrices. AlphaTensor discovered algorithms that outperform the stateoftheart complexity for many matrix sizes. Particularly relevant is the case of 4 × 4 matrices in a finite field, where AlphaTensor’s algorithm improves on Strassen’s twolevel algorithm for the first time since its discovery 50 years ago. In this talk I’ll present the mathematical problem underlying algorithm discovery for matrix multiplication, and our formulation of this problem as a singleplayer game. Then I'll describe general ingredients for tackling mathematical problems using machine learning techniques, and show how these ingredients enable AlphaTensor to learn to play this challenging game well, and thereby to discover faster algorithms for matrix multiplication.

Combinatorics on 10 March 2023 at 14:00
Speaker: Jane Tan (Oxford)
Title: Reconstructing 3D cube complexes from boundary distances
Abstract: TBA

AGATA on 09 March 2023 at 17:00
Speaker: James Timmins (University of Oxford)
Title: Dimensions in noncommutative algebra
Abstract: Due to the dictionary between commutative algebra and algebraic geometry, the
size of commutative algebras and their modules can be measured by the
dimension of geometric objects. In this talk, I’ll describe the picture for
noncommutative algebra, focusing on a fundamental invariant known as
canonical dimension. I’ll illustrate the theory with a classical example that leads
to Bernstein’s inequality, and then describe recent progress for completed group
algebras of padic groups, giving a connection to the (mod p) Langlands
programme. 
Analysis on 09 March 2023 at 16:00
Speaker: Charles Collot (CY Cergy Paris University)
Title: On the soliton resolution for the energy critical wave equation in six dimensions
Abstract: 

Geometry and Topology on 09 March 2023 at 15:00
Speaker: Nansen Petrosyan (Univeristy of Southampton)
Title: Hyperbolicity and Linfinity cohomology
Abstract: Linfinity cohomology is a quasiisometry invariant of finitely generated groups.
It was introduced by Gersten as a tool to find lower bounds for the Dehn
function of some finitely presented groups. I will discuss a generalisation of a
theorem of Gersten on surjectivity of the restriction map in Linfinity
cohomology of groups. This leads to applications on subgroups of hyperbolic
groups, quasiisometric distinction of finitely generated groups and Linfinity
cohomology calculations for some wellknown classes of groups such as RAAGs,
BestvinaBrady groups and Out(F_n). Along the way, we obtain hyperbolicity
criteria for groups of type FP_2(Q) and for those satisfying a rational homological
linear isoperimetric inequality.
I will first define Linfinity cohomology and discuss some of its properties. I will
then sketch some of the main ideas behind the proofs. This is joint work with
Vladimir Vankov. 
Geometry and Topology on 09 March 2023 at 14:00
Speaker: Elia Fioravanti (MPIM Bonn)
Title: Coarse cubical rigidity.
Abstract: When a group G admits nice actions on CAT(0) cube complexes, understanding
the space of all such actions can provide useful information on the outer
automorphism group Out(G). As a classical example, the CullerVogtmann outer
space is (roughly) the space of all geometric actions of the free group F_n on a 1
dimensional cube complex (a tree). In general, however, spaces of cubulations
tend to be awkwardly vast, even for otherwise rigid groups such as the hexagon
RAAG. In an attempt to tame these spaces, we show that all cubulations of many
rightangled Artin and Coxeter groups coarsely look the same, in a strong sense:
they all induce the same coarse median structure on the group. Joint work with
Ivan Levcovitz and Michah Sageev. 
Probability Theory on 08 March 2023 at 16:00
Speaker: Natasha Blitvic (Queen Mary University London)
Title: Combinatorial moment sequences
Abstract: Take your favourite integer sequence. Is this sequence a sequence of moments of some probability measure on the real line? We will look at a number of interesting examples (some proven, others merely conjectured) of moment sequences in combinatorics. We will consider ways in which this positivity may be expected (or surprising!), the methods of proving it, and the consequences of having it. The problems we will consider will be very simple to formulate, but will take us up to the very edge of current knowledge in combinatorics, ‘classical’ probability, and noncommutative probability.

Algebraic Geometry on 08 March 2023 at 15:00
Speaker: Farhad Babaee (Bristol)
Title: Some applications of Tropical Geometry in Complex Geometry
Abstract: In this talk, I will recall two important questions in Complex Analytic Geometry, namely, a strong version of the Hodge Conjecture for Positive Currents and the Equidistribution Conjecture of DinhSibony. I will also explain how Tropical Geometry can provide insight into these questions. No background in these topics is assumed.

Analysis on 08 March 2023 at 14:00
Speaker: Sylvester ErikssonBique (Jyväskylä)
Title: BiLipschitz nonembeddability of nonabelian Carnot groups into L1
Abstract: 

Algebraic Topology on 07 March 2023 at 16:00
Speaker: Ben Briggs (University of Copenhagen)
Title: Syzygies of the cotangent complex
Abstract: The cotangent complex is an important object from commutative algebra. It was defined by Quillen using homotopical methods, and is usually usually extremely difficult to compute. It is connected with some more tractable invariants: the module of differential forms, the conormal module, and Koszul homology can all be seen as syzygies of the cotangent complex. One can try to establish higher analogues of the Jacobian criterion by characterising geometric conditions in terms of homological properties of these syzygies. I will explain how thinking along these lines leads to a new proof of Quillen's conjecture on the cotangent complex and Vasconcelos' conjecture on the conormal module. I'll also try to explain some of the parallels in rational homotopy theory. This is joint work with Srikanth Iyengar.

Number Theory on 06 March 2023 at 15:00
Speaker: Peiyi Cui (East Anglia)
Title: Decompositions of the category of lmodular representations of SL_n(F)
Abstract: Let F be a padic field, and k an algebraically closed field of characteristic l different from p. In this talk, we will first give a category decomposition of Rep_k(SL_n(F)), the category of smooth krepresentations of SL_n(F), with respect to the GL_n(F)equivalent supercuspidal classes of SL_n(F), which is not always a block decomposition in general. We then give a block decomposition of the supercuspidal subcategory, by introducing a partition on each GL_n(F)equivalent supercuspidal class through type theory, and we interpret this partition by the sense of lblocks of finite groups. We give an example where a block of Rep_k(SL_2(F)) is defined with respect to several SL_2(F)equivalent supercuspidal classes, which is different from the case where l is zero. We end this talk by giving a prediction on the block decomposition of Rep_k(A) for a general padic group A.

Colloquium on 03 March 2023 at 16:00
Speaker: Olivia Caramello (University of Insubria, Como; online)
Title: Grothendieck toposes as unifying 'bridges' in Mathematics
Abstract: I will explain the sense in which Grothendieck toposes can act as unifying 'bridges' for relating different mathematical theories to each other and studying them from a multiplicity of points of view. I shall first present the general techniques underpinning this theory and then discuss a number of selected applications in different mathematical fields.

Combinatorics on 03 March 2023 at 14:00
Speaker: Jozef Skokan (LSE)
Title: Separating the edges of a graph by a linear number of paths
Abstract: Recently, Letzter proved that any graph of order n contains a collection P of O(n log^*n) paths with the following property: for all distinct edges e and f there exists a path in P which contains e but not f. We improve this upper bound to 19n, thus answering a question of Katona and confirming a conjecture independently posed by Balogh, Csaba, Martin, and Pluhar and by FalgasRavry, Kittipassorn, Korandi, Letzter, and Narayanan.

Applied Mathematics on 03 March 2023 at 12:00
Speaker: Carina Geldhauser (Lund)
Title: An introduction to point vortex models
Abstract: In this talk we will discuss a family of discrete models for atmospheric turbulence, often called point vortex models. They have been originally derived by Helmholtz, about 130 years ago, but many interesting questions are still open.
We will show how point vortices provide an approximation of solutions to generalized surface quasigeostrophic models, a family of fractional PDEs which interpolate between 2D Euler equations and the more irregular SQG equation.
Lastly, we will briefly touch upon how variational methods and tools from probability theory together can help us to obtain more information about turbulence phenomena. Joint work with Marco Romito (Uni Pisa). 
Analysis on 02 March 2023 at 16:00
Speaker: Fernando GalazGarcía (Durham)
Title: Topology and geometry of 3dimensional Alexandrov spaces
Abstract: 

Junior Analysis and Probability Seminar on 02 March 2023 at 13:00
Speaker: Martin Peev (Imperial College London)
Title: Localising Fermionic (S)PDEs
Abstract: TBA

Probability Theory on 01 March 2023 at 16:00
Speaker: Serge Cohen (University of Toulouse)
Title: Transition of the simple random walk on the graph of the icemodel
Abstract: The 6vertex model is a seminal model for many domains in Mathematics and Physics. The sets of configurations of the 6vertex model can be described as the set of paths in multigraphs. In this article the transition probability of the simple random walk on the multigraphs is computed. The unexpected point of the results is the use of continuous fractions to compute the transition probability.

Algebraic Geometry on 01 March 2023 at 15:00
Speaker: Liana Heuberger (Bath)
Title: QFano threefolds and how to construct them
Abstract: I will give a brief overview about the techniques involved in constructing Fano varieties using mirror symmetry, appearing in the works of Coates, Corti, Kasprzyk et al. I will then describe one of its more concrete incarnations, a method of "inverting" a toric degeneration called Laurent Inversion, which I have used to construct 100 deformation families of QFano threefolds.

Postgraduate on 01 March 2023 at 12:00
Speaker: Patricia Medina Capilla (University of Warwick)
Title: Crowns and their uses in generation problems
Abstract: The generation properties of a group reveal a lot of information about its structure. As such, these properties have been investigated very thoroughly in the last century. This has led to some very beautiful and surprising results being proven, such as the fact that all simple groups are generated by two elements. Relatively recently, Dalla Volta and Lucchini developed the theory of crowns in order to tackle such problems.
In this talk, we will introduce the set of crowns of a group, describe how it is utilised in generation problems, and showcase its strength via some examples. Time allowing, I will explain how this approach has been applied in recent research in order to bound the number of generators of the maximal subgroups of simple groups. 
Algebraic Topology on 28 February 2023 at 16:00
Speaker: Gonçalo Tabuada (Warwick)
Title: Grothendieck classes of quadric hypersurfaces and involution varieties
Abstract: The Grothendieck ring of varieties, introduced in a letter from Alexander Grothendieck to JeanPierre Serre (August 16th 1964), plays an important role in algebraic geometry. However, despite the efforts of several mathematicians, the structure of this ring still remains poorly understood. In this talk, in order to better understand the Grothendieck ring of varieties, I will describe some new structural properties of the Grothendieck classes of quadric hypersurfaces and involution varieties. More specifically, by combining the recent theory of noncommutative motives with the classical theory of motives, I will show that if two quadric hypersurfaces (or, more generally, two involution varieties) have the same Grothendieck class, then they have the same even Clifford algebra and the same signature. As an application, this implies in numerous cases (e.g., when the base field is a local or global field) that two quadric hypersurfaces (or, more generally, two involution varieties) have the same Grothendieck class if and only if they are isomorphic.

Number Theory on 27 February 2023 at 15:00
Speaker: Efthymios Sofos (Glasgow)
Title: Schinzel's Hypothesis on average and the Hasse principle
Abstract: Schinzel's Hypothesis regards prime values taken by a polynomial with integer coefficients. I will talk about work with Skorobogatov where we established that the Hypothesis holds for 100% of cases in a probabilistic sense. I will also talk about joint work with Browning and Teräväinen where we extend the previous result in various directions.

Colloquium on 24 February 2023 at 16:00
Speaker: Steven Tobias (Leeds)
Title: "So Many DynamoS": Some interesting mathematical problems in dynamo theory
Abstract: The generation of magnetic field in the Earth's interior and the origin of the eleven year solar cycle are both thought to lie in hydromagnetic dynamo action. In both cases fluid motions interact with rotation to sustain electrical currents and hence magnetic field. In this talk I will give an introduction to the mathematical structure of the equations for the generation of magnetic field and highlight some interesting unsolved mathematical problems. I'll conclude by drawing an analogy with transition to turbulence in flow down a pipe.

Combinatorics on 24 February 2023 at 14:00
Speaker: Amarja Kathapurkar (University of Birmingham)
Title: Transversal cycle factors in multipartite graphs
Abstract: TBA

Applied Mathematics on 24 February 2023 at 12:00
Speaker: Ellen Luckins (Oxford)
Title: Reactive decontamination of porous media
Abstract: Following a chemical weapons attack, it is crucial for public health that the toxic chemical agent is properly cleaned up. One particular issue is when the agent has contaminated porous materials, such as brick or concrete. In such cases, decontamination is typically achieved by neutralising the agent with a cleanser in a chemical reaction. It is relatively straightforward to write down a model that describes the interplay of the agent and cleanser fluids on the scale of the pores, but very computationally expensive to solve such a model over realistic spill sizes. In this talk I will present homogenised PDE models for the reactive decontamination of porous media, which are computationally efficient to simulate while still taking the porescale behaviour into account. Solutions of these homogenised models show how differences in the initial distribution of agent within the porespace affect both the decontamination time and the amount of cleanser required to fully decontaminate the porous material.

Analysis on 23 February 2023 at 16:00
Speaker: Xavier Tolsa (UAB)
Title: Quantitative FaberKrahn inequalities and Carleson's conjecture in higher dimensions
Abstract: 

Junior Analysis and Probability Seminar on 23 February 2023 at 13:00
Speaker: Dimitri Bytchenkoff (University of Vienna)
Title: Frames and kernel theorems for coorbit spaces
Abstract: TBA

Probability Theory on 22 February 2023 at 16:00
Speaker: Alessandra Occelli (Université d'Angers)
Title: Nonlinear fluctuations of multispecies interacting particle sys
Abstract:
Abstract:
We study the equilibrium fluctuations of an exclusion process evolving on the discrete ring with three species of particles, named A, B and C . We prove that proper choices of the density fluctuation fields (given by linear combinations of the fields associated to the conserved quantities that match the prediction from mode coupling theory [Spohn 2014]) converge, in a suitable large scale limit, to stochastic partial differential equations, that can either be the OrnsteinUhlenbeck equation or the stochastic Burgers equation. Based on a joint work with G. Cannizzaro, P. Gonçalves and R. Misturini. 
Postgraduate on 22 February 2023 at 12:00
Speaker: Hefin Lambley (University of Warwick)
Title: An introduction to inverse problems
Abstract: Given an observed effect, the inverse problem is to determine the cause. These problems are hard to solve because they are unstable: small errors in the observed effect lead to big errors in the reconstructed cause.
I will give some examples of inverse problems and discuss practical ways to solve them. We'll also see how this links to uncertainty quantification, which is an active research topic both for applied mathematicians and for engineers modelling realworld phenomena in the presence of noise and uncertainty. 
LMS HA PDE network meeting on 21 February 2023 at 16:00
Speaker: Matthew Hyde (University of Warwick)
Title: Quantitative rectifiability in metric spaces
Abstract: 

LMS HA PDE network meeting on 21 February 2023 at 15:00
Speaker: Xavier Tolsa (Barcelona)
Title: The regularity problem for the Laplace equation and boundary Poincaré inequalities in rough domains
Abstract: 

LMS HA PDE network meeting on 21 February 2023 at 14:00
Speaker: Annalisa Massaccesi (Padova)
Title: Frobenius theorem for weak submanifolds
Abstract: 

LMS HA PDE network meeting on 21 February 2023 at 13:00
Speaker: Paolo Bonicatto (University of Warwick)
Title: Existence and uniqueness for the Lipschitz transport of normal currents
Abstract: 

Algebra on 20 February 2023 at 17:00
Speaker: Nadia Mazza (Lancaster)
Title: On endotrivial modules
Abstract: Let G be a finite group and k a field of positive characteristic p diving the order of G. An endotrivial kGmodule is a finitely generated kGmodule which is "invertible" in some suitable sense. Since the late 70s, these modules have been intensely studied in modular representation theory. In this talk, we briefly review the background, before presenting some results (joint with Carlson, Grodal and Nakano) about endotrivial modules for some "very important" finite groups.

Number Theory on 20 February 2023 at 15:00
Speaker: Sacha Mangerel ((Durham))
Title: (Durham)
Abstract: A conjecture of Chowla, analogising the HardyLittlewood prime $k$tuples conjecture, predicts that the autocorrelations of $\lambda$ (the completely multiplicative function taking the value 1 at all primes) tend to 0 on average, e.g., $\frac{1}{x}\sum_{n \leq x} \lambda(n+1)\cdots \lambda(n+k) \rightarrow 0 \text{ as } x \rightarrow \infty$.
This conjecture, along with its generalisation to other bounded ``nonpretentious'' multiplicative functions due to Elliott, remain wide open for $k \geq 2$. In this talk I will present an explicit construction of a nonpretentious multiplicative function $f: \mathbb{N} \rightarrow \{1,1\}$ all of whose autocorrelations tend to 0 on average, answering a question of Lemanczyk. I will further discuss the following applications of this construction:
1. a proof that Chowla's conjecture does not imply the Riemann Hypothesis, i.e., there are functions $f$ all of whose autocorrelations tend to 0, but that do not exhibit squareroot cancellation on average (the object of some recent speculation);
2. there are multiplicative subsemigroups of $\mathbb{N}$ with Poissonian gap statistics, thus giving an unconditional multiplicative analogue of a classical result of Gallagher about primes in short intervals.
(Joint work with Oleksiy Klurman, Pär Kurlberg and Joni Teräväinen) 
Colloquium on 17 February 2023 at 16:00
Speaker: Clinton Conley (Carnegie Mellon)
Title: Borel reducibility
Abstract: The idea of comparing the complexity of two equivalence relations on the reals by searching for a _Borel reduction_ from one to the other has transformed the last three decades of descriptive set theory. In addition to making precise the intuitive notion that some classification problems are "harder" than others, it has inspired fruitful connections with other areas of math such as dynamical systems and combinatorics.
We give an introduction to this theory, working through some specific examples and sampling some recent developments. Particular attention will be paid to how group and graphtheoretic notions manifest in the Borel reducibility hierarchy. 
Combinatorics on 17 February 2023 at 14:00
Speaker: Mehtaab Sawhney (MIT)
Title: The existence of subspace designs
Abstract: We prove the existence of subspace designs with any given parameters, provided that the dimension of the underlying space is sufficiently large in terms of the other parameters of the design and satisfies the obvious necessary divisibility conditions. This settles an open problem from the 1970s. Moreover, we also obtain an approximate formula for the number of such designs. Joint w. Peter Keevash and Ashwin Sah.

Applied Mathematics on 17 February 2023 at 12:00
Speaker: Bindi Brook (Nottingham)
Title: Airway remodelling in asthma  the chicken or the egg?
Abstract: Inflammation, airway hyperresponsiveness (which causes constriction of the airways at lower trigger levels than in normal subject) and airway remodelling (long term structural changes of the airway wall) are key features of asthma. While this is wellestablished, it is not clear how they are linked or whether they are causes or symptoms of the disease. In this talk I will give an overview of the multiscale biomechanical models we have developed to understand how smooth muscle contraction at the cell level translates to tissue level airway constriction during an asthma attack. Then I will describe a longtimescale theoretical model, developed in parallel with an experimental study, that accounts for mechanochemical drivers of airway remodelling with some illustrative results. And finally I will describe some work in progress: how the combination of both experimental data and the mechanistic model might be used to understand maintenance of homoeostasis in healthy airways and therefore what perturbations might drive the airway into a diseased state.

Analysis on 16 February 2023 at 16:00
Speaker: Yoshihiro Tonegawa (Tokyo Institute of Technology)
Title: Some existence and uniqueness questions for mean curvature flow
Abstract: 

Probability Theory on 15 February 2023 at 16:00
Speaker: Ellen Powell (University of Durham)
Title: Brownian excursions, conformal loop ensembles and critical Liouville quantum gravity
Abstract: It was recently shown by Aidekon and Da Silva how to construct a growth fragmentation process from a planar Brownian excursion. I will explain how this same growth fragmentation process arises in another setting: when one decorates a certain “critical Liouville quantum gravity random surface” with a conformal loop ensemble of parameter 4. This talk is based on joint work with Juhan Aru, Nina Holden and Xin Sun.

Postgraduate on 15 February 2023 at 12:00
Speaker: Eva Zaat (University of Warwick)
Title: Mathematical modelling of metal forming
Abstract: Metal sheets are everywhere around us; they are used in the architecture of buildings, the manufacturing of transportation and decorative art. Metal sheets are versatile due to the many sizes and shapes they can be deformed in. In this talk we will look into the maths behind metal forming.
We will zoom in on the physical mechanics of elastic bending of sheets. By using a toy problem we will be able to recover the governing equations for a simplified setting. These can be expanded to a system of fourth order nonlinear PDEs that describe the deformation of metals in a continuum mechanics framework. We will finish by looking at more complicated problems and the mathematical challenges they pose. 
Ergodic Theory and Dynamical Systems on 14 February 2023 at 14:00
Speaker: Caroline Series (University of Warwick)
Title: Convergence of spherical averages for Fuchsian groups
Abstract: Suppose given a measure preserving action of a Fuchsian group on a probability space X, together with a real valued function f on X. We prove pointwise convergence of spherical averages, more precisely, averages of f(gx) over all words of length 2n in a fixed set of generators.
We will briefly review previous results which involve either Cesàro averages or are restricted to free groups. The current proof is based on a new variant of the BowenSeries symbolic coding for Fuchsian groups that simultaneously encodes all possible shortest paths representing a given group element. The resulting coding is selfinverse, giving a reversible Markov chain to which methods previously introduced by Bufetov in the free group case may be applied.
This is joint work with Sasha Bufetov and Alexey Klimenko, to appear in Commentarii Math Helvetica. 
Algebra on 13 February 2023 at 17:00
Speaker: Dylan Johnston (University of Warwick)
Title: Homotopy type of SL2 quotients of simple complex Lie groups
Abstract: We say an element X in a Lie algebra g is nilpotent if ad(X) is a nilpotent operator. It is known that G_{ad}orbits of nilpotent elements of a complex semisimple Lie algebra g are in 11 correspondence with Lie algebra homomorphisms \phi: sl2 > g, which are in turn in 11 correspondence with Lie group homomorphisms SL2 > G.
Thus, we may denote the homogeneous space obtained by quotienting G by the image of a Lie group homomorphism SL2 > G by X_v, where v is a nilpotent element in the corresponding G_{ad}orbit.
In this talk we introduce some algebraic and topological tools that one can use to attempt to classify the homogeneous spaces, X_v, up to homotopy equivalence. 
Number Theory on 13 February 2023 at 15:00
Speaker: Nikoleta Kalaydzhieva (UCL)
Title: Properties of the multiple solutions to the polynomial Pell equation
Abstract: In the classical theory, a famous byproduct of the continued fraction expansion of quadratic irrational numbers $\sqrt{D}$ is the solution to Pell's equation for $D$. It is wellknown that, once an integer solution to Pell's equation exists, we can use it to generate all other solutions $(u_n,v_n)$ ($n\in\mathbb{Z}$). Our object of interest is the polynomial version of Pell’s equation, where the integers are replaced by polynomials with complex coefficients. We investigate the factors of $v_n(t)$. In particular, we show that over the complex polynomials, there are only finitely many values of n for which $v_n(t)$ has a repeated root. Restricting our analysis to $\mathbb{Q}[t]$, we give an upper bound on the number of 'new' factors of $v_n(t)$ of degree at most $N$. Furthermore, we show that all 'new' linear rational factors of $v_n(t)$ can be found when $n \leq 3$, and all 'new' quadratic rational factors when $n \leq 6$.

Combinatorics on 10 February 2023 at 14:00
Speaker: Nóra Frankl (Open University)
Title: Helly numbers of exponential lattices
Abstract: The Helly number of a set in the plane is the smallest N such that the following is true. If any N members of a finite family of convex sets contains a point of S, then there is a point of S which is contained in all members of the family. An exponential lattice with base x consists of points whose coordinates are positive integer powers of x. We prove lower and upper bounds on Helly numbers of exponential lattices in terms of x, and we determine their values exactly in some cases. We also consider asymmetric exponential lattices, and characterise those that have finite Helly numbers. Joint work with Gergely Ambrus, Martin Balko, Attila Jung and Márton Naszódi.

Applied Mathematics on 10 February 2023 at 12:00
Speaker: Yunan Yang (ETH)
Title: Benefits of Weighted Training in Machine Learning and PDEbased Inverse Problems
Abstract: Many models in machine learning and PDEbased inverse problems exhibit intrinsic spectral properties, which have been used to explain the generalization capacity and the illposedness of such problems. In this talk, we discuss weighted training for computational learning and inversion with noisy data. The highlight of the proposed framework is that we allow weighting in both the parameter space and the data space. The weighting scheme encodes both a priori knowledge of the object to be learned and a strategy to weight the contribution of training data in the loss function. We demonstrate that appropriate weighting from prior knowledge can improve the generalization capability of the learned model in both machine learning and PDEbased inverse problems.

Analysis on 09 February 2023 at 16:00
Speaker: Tim Laux (Bonn)
Title: A new varifold solution concept for mean curvature flow: Convergence of the AllenCahn equation and weakstrong uniqueness
Abstract: 

Junior Analysis and Probability Seminar on 09 February 2023 at 13:00
Speaker: William O'Regan (University of Warwick)
Title: A selected survey of projection theorems
Abstract: TBA

Probability Seminar on 08 February 2023 at 16:00
Speaker: Nikolay Barashkov (University of Helsinki)
Title: Invariant measure for the Anderson wave equation.
Abstract: The Anderson Hamiltonian is an operator whose potential is given by white noise. The singular nature of the potential requires renormalization, but nevertheless it can be made sense of as a self adjoint operator. In this talk we will study the wave equation associated to the Anderson Hamiltonian. Since Bourgain's work there has been a program of constructing invariant measures for dispersive equations. In this talk we will carry this out for the Anderson wave equation. A key part of the proof is the coupling of an "Anderson GFF" with the "Standard" Gaussian free field.

Algebraic Geometry on 08 February 2023 at 15:00
Speaker: Inder Kaur (Loughborough)
Title: Specialization of dominant maps
Abstract: In the last few years many results on the specialization of rationalilty have been shown. In this talk I will discuss the concept of irrationality and give a short overview of related results. I will then discuss the specialization of dominant maps in smooth families.

Algebraic Topology on 07 February 2023 at 16:00
Speaker: Luca Pol (Regensburg)
Title: Quillen stratification in equivariant homotopy theory
Abstract: Quillen’s celebrated stratification theorem provides a geometric description of the Zariski spectrum of the cohomology ring of any finite group with coefficients in a field in terms of information coming from its elementary abelian psubgroups. The goal of this talk is to discuss an extension of Quillen's result to the world of equivariant tensortriangular geometry. For the category of equivariant modules over a commutative equivariant ring spectrum we obtain a stratification result in the terms of the geometric fixed points equipped with their Weylgroup actions for all subgroups, and hence a classification of localizing tensor ideals. Finally, I will apply these methods to several examples of interests such as Borelequivariant Morava Etheory and equivariant topological Ktheory. This is joint work with Tobias Barthel, Natalia Castellana, Drew Heard and Niko Naumann.

Algebra on 06 February 2023 at 17:00
Speaker: Alastair Litterick (University of Essex)
Title: Representation varieties and rigidity in finite simple groups
Abstract: Building from the nowclassical theorem that every nonabelian finite simple group is 2generated, one can ask much more delicate questions, for instance on the abundance of generating pairs, or on the existence of generating pairs with particular orders, or from particular conjugacy classes.
For groups of Lie type, these questions can be studied using the representation variety Hom(F,G) where F is finitely generated and G is a reductive algebraic group. In work with Ben Martin (Aberdeen), we use the conjugation action of G on Hom(F,G) to interpret generators for groups of Lie type as certain Zariskiclosed orbits. This allows us to prove and generalise a 2010 conjecture of C. Marion, and motivates this as an avenue in the wider study of generating sets in groups of Lie type. 
Number Theory on 06 February 2023 at 15:00
Speaker: Amitay Kamber (Cambridge)
Title: Optimal Lifting for SL_n(Z)
Abstract: Let q be a natural number. The strong approximation theorem for $SL_n(Z)$ says that the modulu $q$ map $SL_n(Z) \to SL_n(Z/qZ)$ is onto.
This leads to the following research problem: Given a parameter T, look at the (finite) set of matrices $B_T:={A\in SL_n(Z) : A \le T}$, where $.$ is some matrix norm. We are interested in understanding the image of $B_T$ in $SL_n(Z/qZ)$, for T a function of q. Such studies were initiated (in a more general context) by Duke–Rudnick–Sarnak, and further developed by many others, notably Gorodnik–Nevo.
We will focus on the problem of covering $SL_n(Z/qZ)$ with the image of $B_T$, and explain the connection of the problem to the Generalized Ramanujan Conjecture in automorphic forms.
Based on a joint work with Subhajit Jana. 
Combinatorics on 03 February 2023 at 14:00
Speaker: Shumin Sun (Warwick)
Title: Factors in quasirandom hypergraphs
Abstract: Given two kgraphs (kuniform hypergraphs) F and H, an Ffactor in H is a set of vertex disjoint copies of F that together covers the vertex set of H. Lenz and Mubayi studied the Ffactor problem in quasirandom kgraphs with minimum degree. They posed the problem of characterizing the kgraphs F such that every sufficiently large quasirandom kgraph with constant edge density and minimum degree contains an Ffactor, and in particular, they showed that all linear kgraphs satisfy this property. We prove a general theorem on Ffactors which reduces the Ffactor problem of Lenz and Mubayi to a natural subproblem Fcover problem. By using this result, we answer the question of Lenz and Mubayi for those F which are kpartite kgraphs, and for all 3graphs.
This is joint work with Laihao Ding, Jie Han, Guanghui Wang, and Wenling Zhou. 
Analysis on 02 February 2023 at 16:00
Speaker: WeiBo Su (Warwick)
Title: Glueing constructions in Lagrangian mean curvature flow
Abstract: 

Algebraic Topology on 31 January 2023 at 16:00
Speaker: Neil Strickland (Sheffield)
Title: Questions around chromatic splitting
Abstract: The Chromatic Splitting Conjecture of Hopkins states that if we take
the sphere spectrum, localise with respect to the Morava Ktheory
K(n), then localise again with respect to E(n1), then the result
splits as a coproduct of 2^n pieces, each of which is a sphere
localised with respect to E(m) for some m < n. This is known to be
false (by work of Beaudry) when n=p=2, but remains open (and
mysterious) in general. We will explain how the conjecture, when
combined with known phenomena such as chromatic fracture squares,
predicts some calculations with a very intricate
combinatorial/algebraic structure. These calculations appear to be
selfconsistent, which could easily have failed to be the case; this
suggests that the conjecture may be true, or closely related to the
truth. 
Algebra on 30 January 2023 at 17:00
Speaker: Miriam Norris (University of Manchester)
Title: Some composition multiplicities for tensor products of irreducible representations of GL(n)
Abstract: Understanding the composition factors of tensor products is an important question in representation theory. In characteristic 0 the classical LittlewoodRichardson coefficients describe the composition factors of both the tensor products of simple CGLn(C)modules and the restriction of simple CGLn(C)modules to some Levi subgroup.
Now let F denote an algebraically closed field of characteristic p > 0. In comparison very little is known about composition factors of tensor products of simple FGLn(F)modules but it is thought that there may still be a relationship with the restriction of simple FGLn(F)modules to some Levi subgroup. In this talk explore and explicit relationship of this kind for tensor products of simple FGLn(F)modules with the wedge square of the dual natural module and see how this might be used to find composition factors. 
Number Theory on 30 January 2023 at 15:00
Speaker: Alex Walker (UCL)
Title: Sums of Hecke Eigenvalues in a Quadratic Sequence
Abstract: Many arithmetic functions which are wellunderstood on average over sets of positive density remain mysterious when considered over sparser sets. For example, it is not known if there are infinitely many primes of the form n^2 + 1. The behavior of the divisor function on quadratic sequences was first studied by Hooley and refined by Bykovskii. More recently, Blomer has asked a similar question for the Hecke eigenvalues of a holomorphic cusp form. In this talk, we show how to strengthen Blomer's error estimate through the use of shifted convolution sums and the spectral theory of (halfintegral weight) automorphic forms.

Colloquium on 27 January 2023 at 16:00
Speaker: Gianluca Crippa (Basel)
Title: Anomalous dissipation in fluid dynamics
Abstract: Kolmogorov's K41 theory of fully developed turbulence advances quantitative predictions on anomalous dissipation in incompressible fluids: although smooth solutions of the Euler equations conserve the energy, in a turbulent regime information is transferred to small scales and dissipation can happen even without the effect of viscosity, and it is rather due to the limited regularity of the solutions. In rigorous mathematical terms, however, very little is known. In a recent work in collaboration with M. Colombo and M. Sorella we consider the case of passivescalar advection, where anomalous dissipation is predicted by the ObukhovCorrsin theory of scalar turbulence. In my talk, I will present the general context and illustrate the main ideas behind our construction of a velocity field and a passive scalar exhibiting anomalous dissipation in the supercritical ObukhovCorrsin regularity regime. I will also describe how the same techniques provide an example of lack of selection for passivescalar advection under vanishing diffusivity, and an example of anomalous dissipation for the forced Euler equations in the supercritical Onsager regularity regime (this last result has been obtained in collaboration with E. Brue', M. Colombo, C. De Lellis, and M. Sorella).

Combinatorics on 27 January 2023 at 14:00
Speaker: Freddie Illingworth (University of Oxford)
Title: Reconstructing a point set from a random subset of its pairwise distances
Abstract: Let $V$ be a set of $n$ points on the real line whose positions are not known. Suppose the distances between pairs of points are revealed onebyone in a uniformly random order. When is it possible to reconstruct a linear portion/almost all/all of $V$ up to isometry? In this talk I will discuss the thresholds for this problem as well as giving a precise hitting time result for complete reconstruction of $V$. This is strongly related to the notion of global rigidity for graphs.
This is based on joint work with António Girão, Lukas Michel, Emil Powierski, and Alex Scott. 
Applied Mathematics on 27 January 2023 at 12:00
Speaker: Graham Benham (Oxford)
Title: From Olympic rowing to gunwale bobbing: Wave drag and wave thrust phenomena
Abstract: In this talk I will discuss different wave phenomena associated with motion on the surface of water. I’ll start with some previous work on waves in Olympic rowing and how to reduce drag, either by tuning the shape of the boat, or by exploiting hysteresis patterns in regions of shallow water. Then I’ll talk about current research within the theme of wavedriven propulsion, i.e. how thrust can be generated from surfing the gradients of a selfgenerated wavefield. This phenomenon occurs across a wide range of scales, from tiny walking droplets in a vibrating bath, to jumping up and down on the sides of a canoe to drive it forwards, also known as gunwale bobbing.

Analysis on 26 January 2023 at 16:00
Speaker: Damian Dabrowski (Jyvaskya)
Title: Quantifying Besicovitch projection theorem
Abstract: 

Geometry and Topology on 26 January 2023 at 14:00
Speaker: Davide Spriano (University of Oxford)
Title: Combinatorial criteria for hyperbolicity
Abstract: Perhaps one of the most fascinating properties of hyperbolic groups is that they admit equivalent definitions coming from different areas of mathematics. In this talk, we will survey some interesting definitions, and discuss a new one that, perhaps surprisingly, was previously unknown, namely that fact that hyperbolicity can be detected by the language of quasigeodesics in the Cayley graph. As an application, we will discuss some progress towards a conjecture of Shapiro concerning groups with uniquely geodesic Cayley graphs.

Junior Analysis and Probability Seminar on 26 January 2023 at 13:00
Speaker: Eduardo Tablate (ICMAT)
Title: Schur multipliers in Schatten von Neumann classes and noncommutative Fourier multipliers
Abstract: TBA

Probability Seminar on 25 January 2023 at 16:00
Speaker: Vittoria Silvestri (Università di Roma La Sapienza)
Title: Explosive growth for a constrained Hastings–Levitov aggregation model
Abstract: The HastingsLevitov (HL) growth models describe the formation of random aggregates in the complex plane via conformal maps. In this talk I will discuss a version of the HL models on the upper half plane, in which the growth is restricted to the cluster boundary. We will see that, although one might expect a shape theorem, this constrained model exhibits explosive behaviour, in that the cluster accumulates infinite diameter as soon as it reaches positive capacity. Based on joint work with Nathanael Berestycki.

Algebraic Geometry on 25 January 2023 at 15:00
Speaker: Roberto Gualdi (Regensburg)
Title: How complicated are the solutions of a system of polynomial equations?
Abstract: A beautiful result due to Bernstein and Kushnirenko allows to predict the number of solutions of a system of Laurent polynomial equations from the combinatorial properties of the defining Laurent polynomials.
In a joint work with Martín Sombra (ICREA and Universitat de Barcelona), we give intuitions for an arithmetic version of such a theorem. In particular, in the easy case of the planar curve x + y + 1 = 0, we show how to guess the arithmetic complexity of the intersection point between this line and its translates by torsion points.
The talk will involve a bit of height theory, special values of the Riemann zeta function and will not forget to pay homage to a piece of British literature. 
Ergodic Theory and Dynamical Systems on 24 January 2023 at 14:00
Speaker: Xiong Jin (Manchester University)
Title: An extension of Hochman and Shmerkin’s projection theorem
Abstract: In this talk I will present an extension of Hochman and Shmerkin’s projection theorem on the product of integermultiplication invariant measures on the unit circle. In the symbolic setting we extend these measures to leftshift invariant measures mapped through onedimensional iterated function systems without any separation conditions. Consequently, we prove that Bernoulli convolutions with logrationally independent parameters are dissonate, i.e., their convolution has the maximal possible dimension. If time allows, I will also mention the extension of H.S. theorem from invariant measures to a class of random measures called Mandelbrot cascades. This leads to an extension of Furstenberg’s sumset conjecture (now a theorem by Hochman and Shmerkin) to some more general random fractal sets.

Algebra on 23 January 2023 at 17:00
Speaker: Michael Bate (University of York)
Title: Simple Modules for Algebraic Groups
Abstract: I will report on current work with David Stewart. In this work we have: a) given a classification of simple modules for algebraic groups over arbitrary fields, which extends wellknown high weight classifications when the field is algebraically closed and/or the group is reductive; b) begun to explore the structure of these simple modules, in particular how they look after extensions of the ground field. The key to progress is to understand socalled "pseudoreductive groups". I will spend most of the talk on an extended example of such a group and its representations, which can be constructed pretty concretely from the simple algebraic group SL_2.

Number Theory on 23 January 2023 at 15:00
Speaker: Elisa Lorenzo García (Neuchâtel)
Title: Lower bound on the maximal number of rational points on curves over finite fields
Abstract: For a long time people have being interested in finding and constructing curves with many points. For genus 1 and genus 2 curves, we know how to construct curves over any finite field of defect less than 1 or 3 (respectively), i.e. with a number of points at distance at most 1 or 3 to the upper bound given by the Hasse–Weil–Serre bound. The case of genus 3 is still open after more than 40 years of research. In this talk I will take a different approach based on the random matrix theory of Katz–Sarnak to prove the existence, for all \epsilon > 0, of curves of genus g over Fq with more than 1 + q + (2g −\epsilon )\sqrt{q} points for q big enough. I will also discuss some explicit constructions as well as some consequences to the Serre obstruction problem (an asymmetric behaviour of the distribution of the trace of the Frobenius for curves of genus 3).
This is a joint work with J. Bergström, E. Howe and C. Ritzenthaler. 
Colloquium on 20 January 2023 at 16:00
Speaker: Daniel Meyer (Liverpool)
Title: Fractal spheres, visual metrics, and rational maps
Abstract: The aim of this talk is to show parallels between different areas of mathematics, namely between complex dynamics, Kleinian groups, and random geometry. A common theme are certain fractal spheres that arise. These are the Brownian map (in the random setting) and spheres equipped with socalled visual metrics in the dynamical setting.
A relevant class of maps in this context are quasisymmetric maps. These map ratios of distances in a controlled way and generalize conformal maps.
A Thurston map is a topological analog of a rational map (i.e., a holomorphic selfmap of the Riemann sphere). Thurston gave a criterion when such a map ``is'' rational. Given such a map f that is expanding, we can equip the sphere with a "visual metric". With respect to this metric, the sphere is a quasisphere if and only if f "is" rational.
This is joint work with Mario Bonk (UCLA). 
Combinatorics on 20 January 2023 at 14:00
Speaker: Amedeo Sgueglia (UCL)
Title: A general approach to rainbow versions of Diractype theorems
Abstract: Given a collection of m hypergraphs on the same vertex set V, a rainbow copy of an medge graph F is a copy of F on V obtained by selecting exactly one edge from each hypergraph of the collection. How large does the minimum degree of each graph in the collection need to be so that it necessarily contains a rainbow copy of F? Each hypergraph in the collection could be the same hypergraph, hence the minimum degree of each of them needs to be large enough to ensure that it individually contains F. In this talk, we discuss a unified approach to this problem by providing a widely applicable sufficient condition for this lower bound to be asymptotically tight. This is general enough to recover many previous results in the area and obtain novel rainbow variants of several classical Diractype results for (powers of) Hamilton cycles.
This is joint work with Pranshu Gupta, Fabian Hamann, Alp Müyesser, and Olaf Parczyk. 
Applied Mathematics on 20 January 2023 at 12:00
Speaker: Bryn Davies (Imperial College)
Title: Are quasicrystals the future of metamaterial waveguides?
Abstract: Characterising the spectra of quasiperiodic patterns is a challenging problem that has attracted the attention of mathematicians for several decades. Metamaterial waveguides achieve spectacular wave control feats through carefully designed geometric patterns. In most applications, these patterns are typically periodic, meaning their spectra can be characterised concisely using FloquetBloch techniques. However, modern techniques for describing quasiperiodic patterns are now sufficiently developed that we can use them when designing metamaterial waveguides for specific applications, thereby greatly enlarging the potential design space. This talk will summarise some recent breakthroughs in the characterisation of spectral gaps in quasiperiodic metamaterials and identify opportunities where this theory can be used in applications. In particular, we will look at applications of quasicrystals to graded energy harvesting devices and symmetryinduced waveguides.

Analysis on 19 January 2023 at 16:00
Speaker: Daniel Meyer (Liverpool)
Title: The solenoid, the Chamanara space, and symbolic dynamics
Abstract: 

Junior Analysis and Probability Seminar on 19 January 2023 at 13:00
Speaker: Iain Souttar (HeriotWatt University)
Title: Uniform in time approximations: Averaging
Abstract: TBA

Algebraic Geometry on 18 January 2023 at 15:00
Speaker: Qaasim Shafi (Birmingham)
Title: Divisors on Logarithmic Mapping Spaces
Abstract: The stable maps compactification of the space of rational, degree d curves in P^r is used to define GromovWitten invariants and is helpful for solving enumerative problems concerning rational curves in projective space. Its geometry is well studied. In particular, its Picard/Class group (over Q) was determined by Pandharipande.
The space of rational, degree d curves in P^r with fixed tangencies to a hyperplane H has a compactification by stable logarithmic maps and is used to define relative (or logarithmic) GromovWitten invariants. In joint work with Patrick KennedyHunt, Navid Nabijou and Wanlong Zheng we determine its Class group and Picard group (over Q). I will highlight some of the differences which arise in the logarithmic case and explain how this is part of a broader programme aimed at understanding the geometry of logarithmic mapping spaces. 
Postgraduate on 18 January 2023 at 12:00
Speaker: Peize Liu (University of Warwick)
Title: Introduction to deformation quantisation and formality
Abstract: In 1997, Kontsevich solved the problem of deformation quantisation on Poisson manifolds, which contributed to his winning of the 1998 Fields Medal.
This talk is an introduction to deformation quantisation. This is an approach of going from classical mechanics to quantum mechanics through deformation of the algebra of smooth functions on the phase space. I will explore the original idea from physics and go through some historical developments. Then I will give a crash course on deformation theory based on differential graded Lie algebras and L∞algebras, and show its connection with deformation quantisation via Kontsevich’s formality theorem. 
Algebraic Topology on 17 January 2023 at 16:00
Speaker: Foling Zou (University of Michigan)
Title: Nonabelian Poincare duality theorem in equivariant factorization homology
Abstract: The factorization homology are invariants of ndimensional manifolds with some fixed tangential structures that take coefficients in suitable Enalgebras. In this talk, I will give a definition for the equivariant factorization homology of a framed manifold for a finite group G by monadic bar construction following KupersMiller. Then I will prove the equivariant nonabelian Poincare duality theorem in this case. As an application, in joint work with Asaf Horev and Inbar Klang, we compute the equivariant factorization homology on equivariant spheres for certain Thom spectra. In particular, we recover a computation of the Real topological Hoschild homology by DottoMoiPatchkoriaReeh.

Number Theory on 16 January 2023 at 15:00
Speaker: Julia Stadlmann (Oxford)
Title: The mean square gap between primes
Abstract: Conditional on the Riemann hypothesis, Selberg showed in 1943 that the average size of the squares of differences between consecutive primes less than x is O(log(x)^4). Unconditional results still fall far short of this conjectured bound: Peck gave a bound of O(x^{0.25+epsilon}) in 1996 and to date this is the best known bound obtained using only methods from classical analytic number theory.
In this talk we discuss how sieve theory (in the form of Harman's sieve) can be combined with classical methods to improve bounds on the number of short intervals which contain no primes, thus improving the unconditional bound on the mean square gap between primes to O(x^{0.23+epsilon}). 
Colloquium on 13 January 2023 at 16:00
Speaker: Tom Hudson (Warwick)
Title: Recent developments in the modelling and theory of crystalline defects
Abstract: Crystalline solids are found all around us, and are made up of atoms arranged in a translationinvariant structure. Although this is a significant part of the story for such materials, crystals also contain many defects which break this symmetry, and it is these defects which turn out to be crucial in determining many of the physical properties of a crystalline material. I will begin by motivating the study of such defects, and provide an overview of the range of physical theories used to model and simulate their behaviour. I will then discuss some of the important recent developments in this area (many of which have a Warwick connection), including both novel machinelearningbased approaches and rigorous mathematical developments.

Combinatorics on 13 January 2023 at 14:00
Speaker: Christian Ikenmeyer (University of Warwick)
Title: Characters of the symmetric group and combinatorial interpretations
Abstract: The character of the symmetric group evaluated at the identity is just the number of standard Young tableaux. We study what happens if we evaluate at other elements. Here the character can attain negative values. Our main result is that the square of the character of the symmetric group has no (unsigned) combinatorial description, unless the polynomial hierarchy collapses to the second level. This also works for the absolute value instead of the square.

Applied Mathematics on 13 January 2023 at 12:00
Speaker: Fabian Spill (Birmingham)
Title: Mechanics, Geometry and Topology of Health and Disease
Abstract: Experimental biologists traditionally study biological functions as well as diseases mostly through their abnormal molecular or cellular features. For example, they investigate genetic abnormalities in cancer, hormonal imbalances in diabetes, or an aberrant immune system in vascular diseases. However, many diseases also have a mechanical component which is critical to their deadliness. Notably, cancer kills mostly through metastasis, where the cancer cells acquire the capability to change their physical attachments and migrate. Such mechanical alterations also change geometrical features, such as the cell shape, or topological features, such as the organisation of vascular networks and cellular neighbourhoods within a tissue.
While some of these mechanical, geometrical or topological features in biology are long known, the traditional perspective is to consider them as emergent from molecular features. However, mechanical, geometrical and topological features can also affect the molecular state of a cell. Therefore, the most complete view of many biological systems is to consider them as a complex mechanochemical systems. Diseases such as cancer are then interpreted as perturbations to this system that cannot be solely explained by considering one feature in isolation (such as a single mutation that ‘causes’ cancer).
I will discuss several examples of systems where this mechanical/geometrical/topological coupling to molecular features plays a crucial role: cells that change their shape, blood vessel cells that open gaps to let cancer cells pass during metastasis, and mitochondria that change their organisation in diabetes. 
Analysis on 12 January 2023 at 16:00
Speaker: Jeffrey Galkowski (UCL)
Title: Weyl laws and closed geodesics on typical manifolds
Abstract: 

Algebraic Geometry on 11 January 2023 at 15:00
Speaker: Jenia Tevelev (University of Massachusetts, Amherst)
Title: Semiorthogonal decompositions of moduli spaces
Abstract: Let C be a smooth projective curve of genus g at least 2 and let N be the moduli space of stable rank 2 vector bundles on C with fixed odd determinant. It is a smooth Fano variety of dimension 3g3, Picard number 1 and index 2. We construct a semiorthogonal decomposition of the bounded derived category of N conjectured by Narasimhan and by Belmans, Galkin and Mukhopadhyay. It has two blocks for each ith symmetric power of C for i = 0,...,g2 and one block for the (g1)st symmetric power. Our proof is based on an analysis of wallcrossing between moduli spaces of stable pairs, combining classical vector bundles techniques with the method of windows. Joint work with Sebastian Torres.

Postgraduate on 11 January 2023 at 12:00
Speaker: Hollis Williams (University of Warwick)
Title: Fourier analysis for rarefied gas flows
Abstract: Fourier analysis is widely used in applied mathematics, engineering and physics. In this talk, we explain how it can be used to derive some new exact solutions for nonequilibrium rarefied gas flows. These flows fall into a regime which is inaccessible both to the Boltzmann and NavierStokes equations, so a different set of equations must be used known as the Grad equations.

Algebraic Topology on 10 January 2023 at 16:00
Speaker: Ismael Sierra (Cambridge)
Title: Homological stability of diffeomorphism groups using Ek algebras
Abstract: I will state some recent results about homological stability of diffeomorphism groups of manifolds and give an outline of their proof. In particular, I will talk about the connection to Ek algebras, and about certain complexes, called "splitting complexes", whose highconnectivities are essential to the proof. Finally I will sketch the proof of the highconnectivity of the splitting complexes, which is the most substantial part of the whole argument.

Ergodic Theory and Dynamical Systems on 10 January 2023 at 14:00
Speaker: Cagri Sert (University of Warwick)
Title: Stationary measures for SL(2,R)actions on homogeneous bundles over flag varieties
Abstract: Let X_{k,d} denote the space of rankk lattices in R^d. Topological and statistical properties of the dynamics of discrete subgroups of G = SL(d,R) on X_{d,d} were described in the seminal works of BenoistQuint. A key step/result in this study is the classification of stationary measures on X_{d,d}. Later, SargentShapira initiated the study of dynamics on the spaces X_{k,d}. When k < d, the space X_{k,d} is of a different nature and a clear description of dynamics on these spaces is far from being established. Given a probability measure \mu Zariskidense in a copy of SL(2,R) in G, we give a classifi cation of stationary measures on X_{k,d} and prove corresponding equidistribution results. In contrast to the results of BenoistQuint, the type of stationary measures that \mu admits depends strongly on the position of SL(2,R) relative to parabolic subgroups of G. I will review the preceding works (BenoistQuint, EskinLindenstrauss, SargentShapira) and discuss main cases and ideas. Joint work with Alexander Gorodnik and Jialun Li.

Number Theory on 09 January 2023 at 15:00
Speaker: Wissam Ghantous (Oxford)
Title: A symmetric triple product padic Lfunction
Abstract: In 2014, Darmon and Rotger define the Garrett–Rankin triple product padic Lfunction and relate it to the image of certain diagonal cycles under the padic Abel–Jacobi map. We introduce a new variant of this padic Lfunction and show that it satisfies symmetry relations, when permuting the three families of modular forms. We also provide computational evidence confirming that it is indeed cyclic when the families of modular forms are evaluated at even weights, and provide counterexamples in the case of odd weights. To do so, we extend Lauder's algorithm (for computing ordinary projections of nearly overconvergent modular forms) to work with nearly overconvergent modular forms and compute projections over spaces of nonzero slope.

Colloquium on 09 December 2022 at 16:00
Speaker: John Baez (UC Riverside)
Title: Category Theory in Epidemiology
Abstract: Category theory provides a general framework for building models of dynamical systems. We explain this framework and illustrate it with the example of "stock and flow diagrams". These diagrams are widely used for simulations in epidemiology. Although tools already exist for drawing these diagrams and solving the systems of differential equations they describe, we have created a new software package called StockFlow which uses ideas from category theory to overcome some limitations of existing software. We illustrate this with code in StockFlow that implements a simplified version of a COVID19 model used in Canada. This is joint work with Xiaoyan Li, Sophie Libkind, Nathaniel Osgood and Evan Patterson.

Combinatorics on 09 December 2022 at 14:00
Speaker: Zoltán Vidnyánszky (Eötvös Loránd University)
Title: Borel combinatorics, the LOCAL model and complexity
Abstract: In the first part of the talk, I will give an overview of the field of Borel combinatorics and its recently uncovered connections to the LOCAL model of distributed computing. Then, I will discuss complexity related aspects of the field. Namely, I will consider the question of how hard it is to decide the existence of Borel homomorphisms from a Borel structure to a given finite structure.

Geometry and Topology on 08 December 2022 at 14:00
Speaker: Ric Wade (University of Oxford)
Title: Autinvariant quasimorphisms on groups
Abstract: For a large class of groups, we exhibit an infinitedimensional space of homogeneous quasimorphisms that are invariant under the action of the automorphism group. This class includes nonelementary hyperbolic groups, infinitelyended finitely generated groups, some relatively hyperbolic groups, and a class of graph products of groups that includes all rightangled Artin and Coxeter groups that are not virtually abelian. Joint work with Francesco FournierFacio.

Probability Seminar on 07 December 2022 at 16:00
Speaker: Adrián Gonzáles Casanova (UNAM)
Title: Sampling Duality
Abstract: Sampling Duality is stochastic duality using a duality function S(n,x) of the form ¨what is the probability that all the members of a sample of size n are of type , given that the number (or frequency) of type  individuals is x¨. Implicitly this technique can be traced back to the work of Pascal. Explicitly it is studied in a paper of Martin Möhle in 1999. We will discuss several examples in which this technique is useful, including Haldane's formula and the long standing open question of the rate of the Muller Ratchet.

Postgraduate on 07 December 2022 at 12:00
Speaker: Elvira Lupoian (University of Warwick)
Title: Jacobians of curves: A brief introduction
Abstract: To any algebraic curve C of genus g, we can associate its Jacobian, a gdimensional abelian variety which is functorially associated to the curve. In this talk, I will define Jacobians, assuming no previous knowledge in the subject and explore some of their properties. If time permits, I will touch on one of the ways in which rational points on a Jacobian can be used to find the set of rational points on the corresponding curve.

Algebraic Topology on 06 December 2022 at 16:00
Speaker: Lucy Yang (Harvard)
Title: A real HochschildKostantRosenberg theorem
Abstract: GrothendieckWitt and real Ktheory are enhancements of Ktheory in the presence of duality data. Similarly to ordinary Ktheory, real Ktheory admits homological approximations, known as real trace theories. In this talk, I will identify a filtration on real Hochschild homology and compute the associated graded in terms of an analogue of de Rham forms. We will see how C₂ genuine equivariant algebra is the natural setting for these theories, provide equivariant enhancements of the cotangent and de Rham complexes, and sketch the proof of the main theorem. This work is both inspired by and builds on that of Raksit.

Partial Differential Equations and their Applications on 06 December 2022 at 12:00
Speaker: Antonio Esposito (University of Oxford)
Title: TBA
Abstract: TBA

Algebra on 05 December 2022 at 17:00
Speaker: Ana Retegan (University of Birmingham)
Title: TBC
Abstract: TBC

Number Theory on 05 December 2022 at 15:00
Speaker: Istvan Kolossvary (St Andrews)
Title: Distance between natural numbers based on their prime signature
Abstract: One can define different metrics between natural numbers based on their unique prime signature. Fixing such a metric, we are interested in the asymptotic growth rate of the arithmetic function L(N) which tabulates the cumulative sum of distances between consecutive natural numbers up to N. In particular, choosing the maximum norm, we will show that the limit of L(N)/N exists and is equal to the expected value of a certain random variable. We also demonstrate that prime gaps exhibit a richer structure than on the traditional number line and pose a number of problems. Joint work with Istvan B. Kolossvary.

Colloquium on 02 December 2022 at 16:00
Speaker: Tara Brendle (Glasgow)
Title: Twists and trivializations: encoding symmetries of manifolds
Abstract: The classification of 2manifolds in the first half of the 20th century was a landmark achievement in mathematics, as was the more recent (and more complicated) classification of 3manifolds completed by Perelman. The story does not end with classification, however: there is a rich theory of symmetries of manifolds, encoded in their mapping class groups. In this talk we will explore some aspects of mapping class groups in dimensions 2 and 3, with a focus on illustrative examples.

Combinatorics on 02 December 2022 at 14:00
Speaker: Bernd Schulze (University of Lancaster)
Title: Geometric Rigidity Theory and Applications
Abstract: In the last two decades or so the subject has become particularly active, drawing on diverse areas of mathematics, and engaging with a growing range of modern applications, such as Engineering, Robotics, ComputerAidedDesign, Molecular Dynamics, and Materials Science.
In the first part of the talk, I will give an introduction to Geometric Rigidity Theory, concentrating on some key combinatorial results and problems for barjoint frameworks, but also describing how these have been extended to some other types of frameworks.
Since many realworld structures are symmetric, a major recent research direction in the field is to study the impact of symmetry on the rigidity and flexibility of barjoint frameworks. I will show how group representation theory can be used to reveal `hidden' infinitesimal motions and states of selfstress in symmetric frameworks that cannot be detected with the standard nonsymmetric counts. Finally, I will show how these symmetrybased methods can be used as a design tool for gridshell structures. This is recent joint work with William Baker, Arek Mazurek and Cameron Millar. 
Applied Mathematics on 02 December 2022 at 12:00
Speaker: Katherine Kamal (Cambridge)
Title: The microhydrodynamics of ultrathin nanoparticles: modelling to predict the "unseen"
Abstract: Graphene nanoparticles are ubiquitous, used in everything from the design of more robust extreme weatherresistance spacecraft to flexibleelectronics tracks. Made from just a few atomic layers, the instantaneous dynamics of these platelike particles in flowing liquids are, experimentally, practically inaccessible. We study theoretically and computationally the microhydrodynamics of dilute suspensions of graphene in a simple viscous shear flow field. In the infinite Péclet number limit, a rigid platelet with the interfacial hydrodynamic slip properties of graphene does not follow the periodic rotations predicted for classical colloidal particles but aligns itself at a slight inclination angle with respect to the flow. This unexpected result is due to the hydrodynamic slip reducing the tangential stress at the grapheneliquid surface. By analysing the FokkerPlank equation for the orientational distribution function for decreasing Péclet numbers, we explore how hydrodynamic slip affects the particle’s orientation and effective viscosity. We find that hydrodynamic slip can dramatically change the average particle’s orientation and effective viscosity. For example, the effective viscosity of a dilute suspension of graphene platelets is predicted to be smaller than the base fluids under certain flow conditions for typical slip length values.

Analysis on 01 December 2022 at 16:00
Speaker: Michael Dymond (Birmingham)
Title: Irregular grids and the pushforward equation
Abstract: 

Probability Seminar on 01 December 2022 at 16:00
Speaker: Sunil Chhita (University of Durham)
Title: Domino Shuffle and Matrix Refactorizations
Abstract: This talk is motivated by computing correlations for domino tilings of the Aztec diamond. It is inspired by two of the three distinct methods that have recently been used in the simplest case of a doubly periodic weighting, that is the twoperiodic Aztec diamond. This model is of particular probabilistic interest due to being one of the few models having a boundary between polynomially and exponentially decaying macroscopic regions in the limit. One of the methods to compute correlations, powered by the domino shuffle, involves inverting the Kasteleyn matrix giving correlations through the local statistics formula. Another of the methods, driven by a WienerHopf factorization for two bytwo matrix valued functions, involves the EynardMehta theorem. For arbitrary weights the WienerHopf factorization can be replaced by an LU and ULdecomposition, based on a matrix refactorization, for the product of the transition matrices. In this talk, we present results to say that the evolution of the face weights under the domino shuffle and the matrix refactorization is the same. This is based on joint work with Maurice Duits (Royal Institute of Technology KTH).

Geometry and Topology on 01 December 2022 at 14:00
Speaker: Koji Fujiwara (Kyoto University)
Title: The rates of growth in a hyperbolic group
Abstract: I discuss the set of rates of growth of a finitely generated group with respect to all its finite generating sets. In a joint work with Sela, for a hyperbolic group, we showed that the set is wellordered, and that each number can be the rate of growth of at most finitely many generating sets up to automorphism of the group. I may discuss its generalization to acylindrically hyperbolic groups.

Algebraic Geometry on 30 November 2022 at 15:00
Speaker: Cancelled (n/a)
Title: n/a
Abstract: n/a

Postgraduate on 30 November 2022 at 12:00
Speaker: Nuno Arala Santos (University of Warwick)
Title: Counting Rational Points on Cubic Surfaces
Abstract: A fundamental problem in Diophantine geometry is to understand the asymptotic behaviour of the number of solutions to a Diophantine equation when we impose a boundedness condition on the variables. We will explain some progress in this problem for equations defining cubic surfaces in 3dimensional space, following Roger HeathBrown.

Algebraic Topology on 29 November 2022 at 16:00
Speaker: Florian Naef (Trinity College Dublin)
Title: Relative intersection product, Whiteheadtorsion and string topology
Abstract: Given a closed oriented manifold one can define an intersection product on the homology. This can be extended to local coefficient, and further made relative to the diagonal. I will explain how such a relative selfintersection product is not homotopy invariant (in contrast to the ordinary intersection product) and how this is picked up by string topology. Eventually, we will identify the error term with the trace of Whitehead torsion. More precisely, we will extract an invariant from a Poincare embedding of the diagonal (in the sense of J. Klein) that is the trace of (a version of) Reidemeister torsion. This is based on joint work with P. Safronov.

Algebra on 28 November 2022 at 17:00
Speaker: Rachel Pengelly (University of Birmingham)
Title: TBC
Abstract: TBC

Number Theory on 28 November 2022 at 15:00
Speaker: Alexandre Maksoud (Paderborn)
Title: The arithmetic of the adjoint of a weight 1 modular form
Abstract: A conjecture of Darmon, Lauder and Rotger expresses padic iterated integrals attached to a pair of weight 1 modular forms (f,g) in terms of padic logarithms of certain units attached to f and g. This talk reports a work in progress in which we explain, in the case where f=g, how to interpret this conjecture as a variant of the GrossStark conjecture for the adjoint of f. This requires studying the specializations of the congruence module attached to a Hida deformation of f.

Colloquium on 25 November 2022 at 16:00
Speaker: Cancelled ()
Title: 
Abstract: 

Applied Mathematics on 25 November 2022 at 12:00
Speaker: Eric Neiva (Collége de France & CNRS)
Title: Unfitted finite element methods: decoupling the mesh from the geometry
Abstract: The finite element method (FEM) approximates a PDE from a variational formulation of the problem. Its standard formulation requires a mesh fitting to the boundary of the geometry of interest. Yet, for many problems of practical interest, the geometry is so intricate that mesh generation requires frequent and timeconsuming manual intervention. Boundaryfitted meshing can be avoided with unfitted or immersed FEMs. The main idea is to embed the geometry in a simple mesh (e.g., a Cartesian grid) and define the discretisation in the cells intersecting the geometry. In this talk, we will describe a novel unfitted FEM that circumvents the classical issue of immersed FEM: illconditioning due small celltogeometry intersections We will discuss its application to early embryo development in animals.

Analysis on 24 November 2022 at 16:00
Speaker: Ewelina Zatorska (Imperial)
Title: Analysis of multiphase PDE models: from fluids to crowds
Abstract: 

Junior Analysis and Probability Seminar on 24 November 2022 at 13:00
Speaker: Giacomo del Nin (University of Warwick)
Title: Isoperimetric shapes in Penrose tilings
Abstract: TBA

Probability Seminar on 23 November 2022 at 16:00
Speaker: PierreFrancois Rodriguez (Imperial College London)
Title: Scaling in lowdimensional longrange percolation models
Abstract: The talk will present recent progress towards understanding the critical behavior of dimensional percolation models exhibiting longrange correlations. The results rigorously exhibit the scaling behavior of various observables of interest and are consistent with scaling theory below the uppercritical dimension (expectedly equal to 6).

Algebraic Geometry on 23 November 2022 at 15:00
Speaker: Jonathan Lai (Imperial)
Title: A Reconciliation of Mutations and Potentials
Abstract: Given a lattice polygon, one can consider the spanning fan to obtain a toric variety. A combinatorial mutation is an operation that takes one polygon to another, which induces a degeneration of one toric variety to the other. One can then attempt to study all toric degenerations of a fixed Fano variety through the study of polygons and their mutations. In another world, a set of algebraic tori can be glued together by birational maps, also called mutations, to form a cluster variety.
In this talk, I will explain a justification coming from mirror symmetry on why these two operations deserve to share the same name (in dimension 2). Given an orbifold del Pezzo surface X, there is a natural cluster variety Y that knows about the polytopes and mutations associated to X. Namely, there is a combinatorial object associated to Y called a scattering diagram, which is a collection of walls inside a vector space. The chambers, which correspond to tori in Y, are precisely the polygons coming from toric degenerations of X. This is based off ongoing joint work with Tim Magee and Ben Wormleighton. 
Postgraduate on 23 November 2022 at 12:00
Speaker: Alexandros Groutides (University of Warwick)
Title: Galois representations attached to elliptic curves and the Open Image Theorem
Abstract: A Galois representation is a homomorphism $\rho:Gal(\bar{K}/K)\longrightarrow Aut(V)$ where $V$ is a finite dimensional vector space or a free module of finite rank. These objects are of great importance in number theory due to their connections with elliptic curves, modular forms and $L$functions. We will introduce the mod$\ell$, $\ell$adic and adelic Galois representations attached to a nonCM elliptic curve and discuss the structure of their image. The $\ell$adic open image does not a priori imply the adelic open image but as we will see, it all boils down to the surjectivity of the more innocent sounding mod$\ell$ representation.

Algebraic Topology on 22 November 2022 at 16:00
Speaker: Irakli Patchkoria (University of Aberdeen)
Title: Morava Ktheory of infinite groups and Euler characteristic
Abstract: Given an infinite discrete group G with a finite model for the classifying space for proper actions, one can define the Euler characteristic of G and the orbifold Euler characteristic of G. In this talk we will discuss higher chromatic analogues of these invariants in the sense of stable homotopy theory. We will study the Morava Ktheory of G and associated Euler characteristic, and give a character formula for the LubinTate theory of G. This will generalise the results of HopkinsKuhnRavenel from finite to infinite groups and the Ktheoretic results of Adem, Lück and Oliver from chromatic level one to higher chromatic levels. Along the way we will give explicit computations for amalgamated products of finite groups, right angled Coxeter groups and certain special linear groups. This is all joint with Wolfgang Lück and Stefan Schwede.

Ergodic Theory and Dynamical Systems on 22 November 2022 at 15:30
Speaker: Tim Austin (UCLA)
Title: Positive sofic entropy without relatively Bernoulli factors.
Abstract: The classical Kolmogorov–Sinai entropy is an invariant of probabilitypreserving transformations. Much of the resulting theory was successfully extended to actions of discrete amenable groups by Ornstein, Weiss and others.
Lewis Bowen’s more recent notion of sofic entropy extends the Kolmogorov–Sinai definition to actions of sofic groups, a much larger class introduced by Gromov. A range of natural questions concern how entropy and its consequences differ between the sofic setting the amenable one.
After reviewing a special case of sofic entropy for certain freeproduct groups, this talk will present a new example of an action of such a group. The example has positive sofic entropy, but has no splitting as a direct product involving a Bernoulli factor. This contrasts with the world of amenable group actions, where many such splittings are guaranteed by the weak Pinsker theorem. The new example is an algebraic action, and its analysis depends on (slight modifications of) results
from the theory of random regular lowdensity paritycheck codes.
This material is part of an ongoing joint project with Lewis Bowen, Brandon Seward and Christopher Shriver.
(This talk will be a continuation of the colloquium from Friday Nov 18th, and will assume some of the notions from that talk.) 
Ergodic Theory and Dynamical Systems on 22 November 2022 at 14:00
Speaker: Timothée Bénard (Cambridge)
Title: The local limit theorem for biased random walks on nilpotent groups
Abstract: We prove the local limit theorem for biased random walks on a simply connected nilpotent Lie group G. The result allows to approximate at scale 1 the nstep distribution of a walk by the time n of a smooth diffusion process for a new group structure on G. We also show this approximation is robust under deviation. The proof uses a Gaussian replacement scheme, combining Fourier analysis and a swapping argument inspired by the work of DiaconisHough. As a consequence, we obtain a probabilistic version of Ratner's theorem: Adunipotent random walks on finitevolume homogeneous spaces equidistribute toward algebraic measures.

Partial Differential Equations and their Applications on 22 November 2022 at 12:00
Speaker: Annika Bach (Sapienza Università di Roma)
Title: TBA
Abstract: TBA

Algebra on 21 November 2022 at 17:00
Speaker: Diego Martin Duro (University of Warwick)
Title: TBC
Abstract: TBC

Number Theory on 21 November 2022 at 15:00
Speaker: Rachel Greenfeld (IAS)
Title: Aperiodicity of translational tilings
Abstract: Translational tiling is a covering of a space using translated copies of some building blocks, called the "tiles", without any positive measure overlaps. What are the possible ways that a space can be tiled?
A well known conjecture in this area is the periodic tiling conjecture, which asserts that any tile of Euclidean space admits a periodic tiling. In a joint work with Terence Tao, we construct a counterexample to this conjecture. In the talk, I will survey the study of the periodicity of tilings and discuss our recent progress. 
Colloquium on 18 November 2022 at 16:00
Speaker: Tim Austin (UCLA)
Title: Some recent developments around entropy in ergodic theory
Abstract: The entropy rate of a stationary sequence of random symbols was introduced by Shannon in his foundational work on information theory in 1948. In the early 1950s, Kolmogorov and Sinai realized that they could turn this quantity into an isomorphism invariant for measurepreserving transformations on a probability space. Almost immediately, they used it to distinguish many examples called "Bernoulli shifts" up to isomorphism. This resolved a famous open question of the time, and ushered in a new era for ergodic theory.
In the decades since, entropy has become one of the central concerns of ergodic theory, having widespread consequences both for the abstract structure of measurepreserving transformations and for their behaviour in applications. In this talk, I will review some of the highlights of the structural story, and then discuss Bowen's more recent notion of `sofic entropy'. This generalizes KolmogorovSinai entropy to measurepreserving actions of many `large' nonamenable groups including free groups. I will end with a recent result illustrating how the theory of sofic entropy has some striking differences from its older counterpart.
This talk will be aimed at a general mathematical audience. Most of it should be accessible given a basic knowledge of measure theory, probability, and a little abstract algebra. 
Combinatorics on 18 November 2022 at 14:00
Speaker: Shoham Letzter (UCL)
Title: Separating paths systems of almost linear size
Abstract: A separating path system for a graph G is a collection P of paths in G such that for every two edges e and f, there is a path in P that contains e but not f. We show that every nvertex graph has a separating path system of size O(n log* n). This improves upon the previous best upper bound of O(n log n), and makes progress towards a conjecture of FalgasRavry–Kittipassorn–Korándi–Letzter–Narayanan and Balogh–Csaba–Martin–Pluhár, according to which an O(n) bound should hold.

Applied Mathematics on 18 November 2022 at 12:00
Speaker: Anna Song (Imperial)
Title: Describing tubular shapes and branching membranes with geometry and topology
Abstract: Tubular and membranous shapes are important mathematical structures that arise in many biomedical applications. Morphology is linked to function: their branching patterns, shaped by interactions and remodelled by diseases, inform us on a biological system.
I will present the “curvatubes” model, which unifies a wide continuum of porous shapes within a common geometric framework (https://doi.org/10.1007/s10851021010499). It generalizes the Helfrich model for biomembranes by considering shapes as optimizers of a curvature functional in which the principal curvatures may play asymmetric roles. The geometric problem is approximated by a novel phasefield formulation that satisfies a Gammalimsup property, and is readily implementable as a GPU algorithm. The framework is very flexible and shape textures can be aligned, spatialized, or constrained on a domain.
In the remaining time, I will introduce some topological approaches to analyze such structures using persistent homology, and how they may empirically quantify the "texture of shapes". These are tested on proprietary images of bone marrow vasculature remodelled in acute myeloid leukaemia.
Overall, these compact descriptions offer a unified view to branching tubules and membranes, and will potentially lead to applications in bioengineering, imaging, or materials science. 
Analysis on 17 November 2022 at 16:00
Speaker: Max Stolarski (Warwick)
Title: Closed Ricci Flows with Singularities Modeled on Asymptotically Conical Shrinkers
Abstract: 

Geometry and Topology on 17 November 2022 at 14:00
Speaker: Bradley Zykoski (Univeristy of Michigan)
Title: A polytopal decomposition of strata of translation surfaces
Abstract: A closed surface can be endowed with a certain locally Euclidean metric structure called a translation surface. Moduli spaces that parametrize such structures are called strata. There is a GL(2,R)action on strata, and orbit closures of this action are rare gems, the classification of which has been given a huge boost in the past decade by landmark results such as the "Magic Wand" theorem of EskinMirzakhaniMohammadi and the Cylinder Deformation theorem of Wright. Investigation of the topology of strata is still in its nascency, although recent work of CalderonSalter and CostantiniMöllerZachhuber indicate that this field is rapidly blossoming. In this talk, I will discuss a way of decomposing strata into finitely many higherdimensional polytopes. I will discuss how I have used this decomposition to study the topology of strata, and my ongoing work using this decomposition to study the orbit closures of the GL(2,R)action.

Junior Analysis and Probability Seminar on 17 November 2022 at 13:00
Speaker: Jakub Takác (University of Warwick)
Title: Norms in finite dimensions and rectifiability in metric spaces
Abstract: TBA

Probability Seminar on 16 November 2022 at 16:00
Speaker: Sam OleskerTaylor (University of Warwick)
Title: Random Walks on Random Cayley GraphsTBA
Abstract: TBAhttps://teams.microsoft.com/l/meetupjoin/19%3ameeting_Mjg1MDU2MDQtY2NlZS00Y2NlLWFhNWUtZWRiMmEwYjI0ZGEz%40thread.v2/0?context=%7b%22Tid%22%3a%2209bacfbd47ef446592653546f2eaf6bc%22%2c%22Oid%22%3a%22325bf9e5c56a4d319811aa22fe105e13%22%7d
Join conversation
teams.microsoft.com
We investigate mixing properties of RWs on random Cayley graphs of a finite group G with
k≫ 1 independent, uniformly random generators, with 1 ≪ log k ≪ log G.
Aldous and Diaconis (1985) conjectured that the RW on this random graph exhibits cutoff for any group G whenever k ≫ log G and further that the cutoff time depends only on k and G. It was established for Abelian groups.
We disprove the second part of the conjecture by considering RWs on uppertriangular matrices. We extend this conjecture to 1 ≪ k ≲ log G, verifying a version of it for arbitrary Abelian groups under 'almost necessary' conditions on k.
It is all joint work with Jonathan Hermon (now at UBC). 
Algebraic Geometry on 16 November 2022 at 15:00
Speaker: Ruijie Yang (HumboldtUniversität zu Berlin)
Title: Zeroes of one forms and homologically trivial deformations
Abstract: In 1926, Hopf proved the PoincaréHopf theorem, which implies that if a compact differential manifold admits a nowhere vanishing vector field, then its topological Euler characteristic is zero. Dually, it is natural to ask the same question for one forms. In 1970, Tischler proved that the existence of a nowhere vanishing real closed one form induces a differentiable fiber bundle structure over the circle. In 2013, Kotschick conjectured that for compact Kähler manifolds, admitting a nowhere vanishing real closed one form is actually equivalent to the existence of a nowhere vanishing holomorphic one form. In this talk, I will show that Kotschick’s conjecture can be deduced from a conjecture of BobadillaKollár on homologically trivial deformation. Therefore, Kotschick’s conjecture is true if the first Betti number of X is at least 2dim(X)2 and the Albanese variety of X is simple. This is joint work with Stefan Schreieder.

Postgraduate on 16 November 2022 at 12:00
Speaker: Andrew Ronan (University of Warwick)
Title: Exact couples and nilpotent spaces
Abstract: We will introduce spectral sequences via exact couples and outline how to derive the Serre spectral sequence from algebraic topology. Then, we will introduce nilpotent spaces, which are a type of space in many ways dual to a CW complex, before explaining how the Serre spectral sequence can be used to derive some of their properties. For example, the homology groups of a nilpotent space are finitely generated if and only if its homotopy groups are finitely generated.

Algebraic Topology on 15 November 2022 at 16:00
Speaker: Foling Zou (University of Michigan)
Title: Nonabelian Poincare duality theorem in equivariant factorization homology
Abstract: The factorization homology are invariants of ndimensional manifolds with some fixed tangential structures that take coefficients in suitable Enalgebras. In this talk, I will give a definition for the equivariant factorization homology of a framed manifold for a finite group G by monadic bar construction following KupersMiller. Then I will prove the equivariant nonabelian Poincare duality theorem in this case. As an application, in joint work with Asaf Horev and Inbar Klang, we compute the equivariant factorization homology on equivariant spheres for certain Thom spectra. In particular, we recover a computation of the Real topological Hoschild homology by DottoMoiPatchkoriaReeh.

Ergodic Theory and Dynamical Systems on 15 November 2022 at 14:00
Speaker: Mar Giralt (Universitat Politecnica de Catalunya)
Title: Chaotic dynamics, exponentially small phenomena and Celestial Mechanics
Abstract: A fundamental problem in dynamical systems is to prove that a given model has chaotic dynamics. One of the methods employed to prove this type of motions is to verify the existence of transversal intersections between the stable and unstable manifolds of certain objects. Then, there exists a theorem (the SmaleBirkhoff homoclinic theorem) which ensures the existence of chaotic motions. In this talk we present a method to analyze the distance and transversality between certain stable and unstable manifolds when a small perturbation is added to an integrable system. In particular, we consider the case where the distance between manifolds is exponentially small. This implies that this difference cannot be detected by expanding the manifolds into a series with respect to the small perturbation parameter. Therefore, classical perturbation theory cannot be applied. Finally, we apply these techniques to a celestial mechanics problem. In particular, we study the Lagrange point L_3 in the restricted planar circular 3body problem.

Algebra on 14 November 2022 at 17:00
Speaker: Jay Taylor (University of Manchester)
Title: TBC
Abstract: TBC

Number Theory on 14 November 2022 at 15:00
Speaker: Rosa Winter (KCL)
Title: Density of rational points on del Pezzo surfaces of degree 1
Abstract: Let X be an algebraic variety over an infinite field k. In arithmetic geometry we are interested in the set X(k) of krational points on X. For example, is X(k) empty or not? And if it is not empty, is X(k) dense in X with respect to the Zariski topology?
Del Pezzo surfaces are surfaces classified by their degree d, which is an integer between 1 and 9 (for d >= 3, these are the smooth surfaces of degree d in P^d). For del Pezzo surfaces of degree at least 2 over a field k, we know that the set of krational points is Zariski dense provided that the surface has one krational point to start with (that lies outside a specific subset of the surface for degree 2). However, for del Pezzo surfaces of degree 1 over a field k, even though we know that they always contain at least one krational point, we do not know if the set of krational points is Zariski dense in general.
I will talk about density of rational points on del Pezzo surfaces, state what is known so far, and show a result that is joint work with Julie Desjardins, in which we give sufficient and necessary conditions for the set of krational points on a specific family of del Pezzo surfaces of degree 1 to be Zariski dense, where k is finitely generated over Q. 
Colloquium on 11 November 2022 at 16:00
Speaker: Yan Fyodorov (King's College London)
Title: "Escaping the crowds": extreme values and outliers in rank1 nonnormal deformations of GUE/CUE
Abstract: Rank1 nonnormal deformations of GUE/CUE provide the simplest model for describing resonances in a quantum chaotic system decaying via a single open channel. In the case of GUE we provide a detailed description of an abrupt restructuring of the resonance density in the complex plane as the function of channel coupling, identify the critical scaling of typical extreme values, and finally describe how an atypically broad resonance (an outlier) emerges from the crowd. In the case of CUE we are further able to study the Extreme Value Statistics of the ''widest resonances'' and find that in the critical regime it is described by a distribution nontrivially interpolating between Gumbel and Frechet. The presentation will be based on the joint works with Boris Khoruzhenko and Mihail Poplavskyi.

Combinatorics on 11 November 2022 at 14:00
Speaker: Adva Mond (University of Cambridge)
Title: Minimum degree edgedisjoint Hamilton cycles in random directed graphs
Abstract: At most how many edgedisjoint Hamilton cycles does a given directed graph contain? A trivial upper bound is the minimum between the minimum out and indegrees. We show that a typical random directed graph D(n,p) contains precisely this many edgedisjoint Hamilton cycles, given that p >= (log^3 n)/n, which is optimal up to a factor of log^

Applied Mathematics on 11 November 2022 at 12:00
Speaker: Fabian Spill  POSTPONED TO TERM 2 (Birmingham)
Title: Mechanics, Geometry and Topology of Health and Disease
Abstract: TBAExperimental biologists traditionally study biological functions as well as diseases mostly through their abnormal molecular or cellular features. For example, they investigate genetic abnormalities in cancer, hormonal imbalances in diabetes, or an aberrant immune system in vascular diseases. However, many diseases also have a mechanical component which is critical to their deadliness. Notably, cancer kills mostly through metastasis, where the cancer cells acquire the capability to change their physical attachments and migrate. Such mechanical alterations also change geometrical features, such as the cell shape, or topological features, such as the organisation of vascular networks and cellular neighbourhoods within a tissue.
While some of these mechanical, geometrical or topological features in biology are long known, the traditional perspective is to consider them as emergent from molecular features. However, mechanical, geometrical and topological features can also affect the molecular state of a cell. Therefore, the most complete view of many biological systems is to consider them as a complex mechanochemical systems. Diseases such as cancer are then interpreted as perturbations to this system that cannot be solely explained by considering one feature in isolation (such as a single mutation that ‘causes’ cancer).
I will discuss several examples of systems where this mechanical/geometrical/topological coupling to molecular features plays a crucial role: cells that change their shape, blood vessel cells that open gaps to let cancer cells pass during metastasis, and mitochondria that change their organisation in diabetes. 
Analysis on 10 November 2022 at 16:00
Speaker: Jean Lagace (Kings)
Title: Spectral geometry on surfaces via conformal maps
Abstract: 

Mathematics Teaching and Learning on 10 November 2022 at 16:00
Speaker: Edmund Robertson (St. Andrews)
Title: MacTutor – a collection of great mathematicians?
Abstract: In my talk I will look at questions such as: Is MacTutor a collection of great mathematicians? What is a “great mathematician?” How did I choose whom to write about?

Junior Analysis and Probability Seminar on 10 November 2022 at 13:00
Speaker: Simon Gabriel (University of Warwick)
Title: On the Poisson–Dirichlet diffusion and Trotter–Kurtz approximations
Abstract: TBA

Probability Seminar on 09 November 2022 at 16:00
Speaker: Kevin Yang (UC Berkeley)
Title: Timedependent KPZ equation from nonequilibrium GinzburgLandau SDEs
Abstract: This talk has two goals. The first is the derivation of a timedependent KPZ equation (TDKPZ) from a timeinhomogeneous GinzburgLandau model. To our knowledge, said TDKPZ has not yet been derived from microscopic considerations. It has a nonlinear twist that is not seen in the usual KPZ equation, making it a more interesting SPDE.
The second goal is the universality of the method (for deriving TDKPZ), which should work beyond GinzburgLandau. In particular, we answer a question of deriving (TD)KPZ from asymmetric particle systems under natural fluctuationscale versions of the assumptions in Yau’s relative entropy method and a logSobolev inequality. This gives some progress on open questions posed at a workshop on KPZ at the American Institute of Math. Time permitting, future directions (of both pure and applied mathematical flavors) will be discussed. 
Algebraic Geometry on 09 November 2022 at 15:00
Speaker: Beihui Yuan (Swansea)
Title: 16 Betti diagrams of Gorenstein CalabiYau varieties and a Betti stratification of Quaternary Quartic Forms
Abstract: Motivated by the question of finding all possible projectively normal CalabiYau 3folds in 7dimensional projective spaces, we proved that there are 16 possible Betti diagrams for arithmetically Gorenstein ideals with regularity 4 and codimension 4. Among them, 8 Betti diagrams have been identified with those of CalabiYau 3folds appeared in a list of 11 families founded by CoughlanGolebiowskiKapustkaKapustka. Another 8 cannot be Betti diagrams of any smooth irreducible nondegenerate 3fold. Based on the apolarity correspondence between Gorenstein ideals and homogeneous polynomials, and on our results on 16 Betti diagrams, we describe a stratification of the space of quartic forms in four variables.
This talk is based on the paper “CalabiYau threefolds in P^n and Gorenstein rings” by Hal Schenck, Mike Stillman and Beihui Yuan, and the preprint “Quaternary quartic forms and Gorenstein rings” by Michal and Grzegorz Kapustka, Kristian Ranestad, Hal Schenck, Mike Stillman and Beihui Yuan. 
Algebraic Topology on 08 November 2022 at 16:00
Speaker: Thibault Décoppet (Oxford)
Title: Fusion 2Categories associated to 2groups
Abstract: Motivated by the cobordism hypothesis, which provides a correspondence between fully dualizable objects and fully extended framed TQFTs, it is natural to seek out interesting examples of fully dualizable objects. In dimension four, the fusion 2categories associated to 2groups are examples of fully dualizable objects. In my talk, I will begin by reviewing the 2categorical notion of Cauchy completion, and recall the definition of a fusion 2category in detail. Then, I will explain how one can construct a fusion 2category of 2vector spaces graded by 2group, and how this construction can be twisted using a 4cocycle. Finally, it is important to understand when two such fusion 2categories yield equivalent TQFTs. The answer is provided by the notion of Morita equivalence between fusion 2categories, which will be illustrated using some examples.

Number Theory on 08 November 2022 at 15:00
Speaker: George Boxer (Imperial)
Title: Higher Hida theory for Siegel modular varieties
Abstract: The goal of higher Hida theory is to study the ordinary part of coherent cohomology of Shimura varieties integrally. We introduce a higher coherent cohomological analog of Hida's space of ordinary padic modular forms, which is defined as the ordinary part of the coherent cohomology with "partial compact support" of the ordinary Igusa variety. Then we give an analog of Hida's classicality theorem in this setting. This is joint work with Vincent Pilloni.

Ergodic Theory and Dynamical Systems on 08 November 2022 at 14:00
Speaker: Donald Robertson (University of Manchester)
Title: Dynamical Cubes and Ergodic Theory
Abstract: n recent works Kra, Moreira, Richter and I showed that positive density sets always contain sums of any finite number of infinite sets, and a shift of the selfsum of an infinite set. The main step in our approach was to prove the existence of certain dynamical configurations described via limit points of orbits. In this talk I will describe what these configurations are, and explain how ergodic theory can be used to deduce their existence.

Partial Differential Equations and their Applications on 08 November 2022 at 12:00
Speaker: Angeliki Menegaki (IHES)
Title: TBA
Abstract: TBA

Algebra on 07 November 2022 at 17:00
Speaker: Michael Bate (University of York)
Title: TBC
Abstract: TBC

Colloquium on 04 November 2022 at 16:00
Speaker: Giovanni Alberti (Pisa)
Title: Small sets in Geometric Measure Theory and Analysis
Abstract: Many relevant problems in Geometric Measure Theory can be ultimately understood in terms of the structure of certain classes of sets, which can be loosely described as "small" (in some sense or another). In this talk I will review a few of these problems and related results, and highlight the connections to other areas of Analysis.

Combinatorics on 04 November 2022 at 14:00
Speaker: Alp Müyesser (UCL)
Title: Hypergraphs defined by groups
Abstract: This talk will be about a genre of problems where one looks for spanning structures in hypergraphs where vertices represent group elements, and edges represent solutions to systems of equations. Problems expressible using this framework include the HallPaige conjecture, the nqueens problem, the harmonious labelling conjecture, Snevily's subsquare conjecture, and many others. We will discuss an absorptionbased attack on problems of this type which has resolved many longstanding conjectures in the area.
Joint work with Alexey Pokrovskiy. 
Applied Mathematics on 04 November 2022 at 12:30
Speaker: Emma Davis (Warwick)
Title: Using compartmental ODE models to forecast the elimination of macroparasitic diseases
Abstract: Standard compartmental models of infectious disease transmission work by categorising a population by stage of infection and then building a system of differential equations that govern the density or number of individuals in each category, e.g. the SIR model has compartments for susceptible (S), infectious (I) and recovered/removed (R) individuals. This makes sense when we are interested in the number of individuals infected over an epidemic where infection is a binary state, as measured by prevalence and incidence, but is less useful for macroparasitic diseases, where infection is instead classified by the number of macroparasites inhabiting any given individual. Models for macroparasitic diseases therefore more commonly consider the number of parasites per individual (their parasite “burden”) or, on a population scale, the mean parasite burden. Common biological features of macroparasitic diseases, such as sexual reproduction of the parasites or indirect transmission routes, and aggregation between individuals, can result in interesting dynamics at low prevalence, which I will discuss using the example of the macroparasitic disease lymphatic filariasis.

Applied Mathematics on 04 November 2022 at 12:00
Speaker: Christian VaqueroStainer (Warwick)
Title: The sedimentation dynamics of thin, rigid disks
Abstract: Sedimentation problems arise in a wide range of natural and industrial processes and exhibit a rich array of phenomenology. A particular motivation for this study is the size segregation of graphene flakes, for which a dominant method is centrifugation in a viscous fluid (Khan 2012). We present a numerical investigation of the sedimentation dynamics of thin, deformed circular disks sedimenting freely under gravity in an otherwise quiescent, Stokesian fluid. In the first part of this study, we address singularities which arise in the fluid pressure and velocity gradient at the edge of the disk, by developing an augmented finite element method to capture the singularities with analytic functions. In the second part of the study, we deploy this method in a fluidstructure interaction framework to examine the behaviour of two distinct classes of disk shape, namely cylindrically and conicallydeformed disks with one and two planes of symmetry, respectively. We explore the geometrydriven dynamics and the bifurcation structure which arises for the conicallydeformed disk as the level of asymmetry is varied.

Analysis on 03 November 2022 at 16:00
Speaker: Luke Peachey (Warwick)
Title: Nonuniqueness in curve shortening flow
Abstract: 

Geometry and Topology on 03 November 2022 at 14:00
Speaker: Becca Winarski (College of the Holy Cross)
Title: Polynomials, branched covers, and trees
Abstract: Thurston proved that a postcritically finite branched cover of the plane is either equivalent to a polynomial (that is: conjugate via a mapping class) or it has a topological obstruction. We use topological techniques – adapting tools used to study mapping class groups – to produce an algorithm that determines when a branched cover is equivalent to a polynomial, and if it is, determines which polynomial a topological branched cover is equivalent to. This is joint work with Jim Belk, Justin Lanier, and Dan Margalit.

Probability Seminar on 02 November 2022 at 16:00
Speaker: Alessandra Cipriani (University College London)
Title: Properties of the gradient squared of the Gaussian free field
Abstract: TBA

Algebraic Geometry on 02 November 2022 at 15:00
Speaker: Michel van Garrel (Birmingham)
Title: Log Mirror Symmetry
Abstract: Start with a smooth Fano variety X and a smooth anticanonical divisor D. Consider the problem of counting maps from the projective line to X that meet D along a curve in only one point. While this problem is intractable directly, in this joint work with Helge Ruddat and Bernd Siebert, we use toric dualities to translate the problem into a dual problem in a dual geometry. There the problem turns into a problem of computing period integrals, which we can readily solved via the techniques of PicardFuchs equations.
In my talk, I will limit to the case of X the projective plane and D a smooth conic. The beforementioned toric dualities are the constructions of the GrossSiebert programme. I hope to convey the observation that the dualities are natural and that the translation from counting problem to period integral is as well. 
Ergodic Theory and Dynamical Systems on 01 November 2022 at 14:00
Speaker: Carlos Matheus (Ecole Polytechnique)
Title: Elliptic dynamics on certain SU(2) and SU(3) character varieties
Abstract: In this talk, we discuss the action of a hyperbolic element of SL(2,Z) on the SU(2) and SU(3) character varieties of oncepunctured torii. This is based on a joint work with G. Forni, W. Goldman and S. Lawton.

Algebra on 31 October 2022 at 17:00
Speaker: Sean Eberhard (University of Cambridge)
Title: The BostonShalev conjecture for conjugacy classes
Abstract: The BostonShalev conjecture (proved by Fulman and Guralnick in 2015) asserts that in any nonabelian simple group G in any nontrivial permutation action the proportion of derangements is at least some absolute constant c > 0. Since the set of derangements is closed under conjugacy it is also natural to ask about the proportion of *conjugacy classes* containing derangements. It is easy to see that this version of the question has a negative answer for alternating groups, but Guralnick and Zalesski asked whether it holds for groups of Lie type. I will outline a proof. We can also (1) extend to the case of almost simple groups, which is not true for the original conjecture, and (2) deduce the original conjecture, which amounts to a simplification of the FulmanGuralnick proof. The key turns out to be a kind of analytic number theory for palindromic polynomials. This is ongoing work with Daniele Garzoni.

Number Theory on 31 October 2022 at 15:00
Speaker: Yoav Gath (Cambridge)
Title: Lattice point statistics for Cygan–Koranyi balls
Abstract: Euclidean lattice point counting problems, the classical example of which is the Gauss circle problem, are an important topic in classical analysis and have been the driving force behind much of the developments in the area of analytic number theory in the 20th century. In this talk, I will introduce the lattice point counting problem for (2q+1)dimensional Cygan–Koranyi balls, namely, the problem of establishing error estimates for the number of integer lattice points lying inside Heisenberg dilates of the unit ball with respect to the Cygan–Koranyi norm. I will explain how this problem arises naturally in the context of the Heisenberg groups, and how it relates to the Euclidean case (and in particular to the Gauss circle problem). I will survey some of the major results obtained to date for this lattice point counting problem, and in particular, results related to the fluctuating nature of the error term.

Colloquium on 28 October 2022 at 16:00
Speaker: Tom Gur (Warwick Computer Science)
Title: Quantum algorithms and additive combinatorics
Abstract: I will discuss a new connection between quantum computing and additive combinatorics, which allows for boosting the power of quantum algorithms. Namely, I will show a framework that uses generalisations of Bogolyubov’s lemma and Sander’s quasipolynomial BogolyubovRuzsa lemma to transform quantum algorithms that are only correct on a small number of inputs into quantum algorithms that are correct on all inputs.

Applied Mathematics on 28 October 2022 at 12:00
Speaker: Maciej Buze (Birmingham)
Title: Mathematical analysis of atomistic fracture and related phenomena in crystalline materials
Abstract: The modelling of atomistic fracture and related phenomena in crystalline materials poses a string of mathematically nontrivial and exciting challenges, both on the theoretical and practical level. At the heart of the problem lies a discrete domain of atoms (a lattice), which exhibits spatial inhomogeneity induced by the crack surface, particularly pronounced in the vicinity of the crack tip. Atoms interact in a highly nonlinear way, resulting in a severely nonconvex energy landscape facilitating nontrivial behaviour of atoms such as (i) crack propagation; (ii) nearcrack tip plasticity  emission and movement of defects known as dislocations in the vicinity of the crack tip; (iii) surface effects  atoms at the crack surface relaxing or possibly attaining an altogether different crystalline structure. On the practical side, the richness of possible phenomena renders the task of setting up numerical simulations particularly tricky  numerical artefacts, e.g. induced by prescribing a particular boundary condition, can lead to inconsistent results. In this talk I will aim to summarise ongoing efforts aimed at putting the atomistic modelling of fracture on a rigorous mathematical footing. I will introduce a framework giving rise to welldefined models for which regularity and stability of solutions can be discussed (topic of my PhD thesis at Warwick). I will then show how the theory can be used to set up practical simulations, such as Mode I fracture of silicon on the (111) cleavage plane using stateoftheart interatomic potentials. I will also outline how this framework can be used to rigorously derive upscaled models of nearcracktip plasticity. Finally, I will also talk about challenges in addressing the surface effects.

Geometry and Topology on 27 October 2022 at 14:00
Speaker: Daniel Berlyne (University of Bristol)
Title: Braid groups of graphs
Abstract: The braid group of a space X is the fundamental group of its configuration space, which tracks the motion of some number of particles as they travel through X. When X is a graph, the configuration space turns out to be a special cube complex, in the sense of Haglund and Wise. I show how these cube complexes are constructed and use graph of groups decompositions to provide methods for computing braid groups of various graphs, as well as criteria for a graph braid group to split as a free product. This has various applications, such as characterising various forms of hyperbolicity in graph braid groups and determining when a graph braid group is isomorphic to a rightangled Artin group.

Algebraic Geometry on 26 October 2022 at 15:00
Speaker: Arman Sarikyan (Edinburgh)
Title: On the Rationality of FanoEnriques Threefolds
Abstract: A threedimensional nonGorenstein Fano variety with at most canonical singularities is called a FanoEnriques threefold if it contains an ample Cartier divisor that is an Enriques surface with at most canonical singularities. There is no complete classification of FanoEnriques threefolds yet. However, L. Bayle has classified FanoEnriques threefolds with terminal cyclic quotient singularities in terms of their canonical coverings, which are smooth Fano threefolds in this case. The rationality of FanoEnriques threefolds is an open classical problem that goes back to the works of G. Fano and F. Enriques. In this talk we will discuss the rationality of FanoEnriques threefolds with terminal cyclic quotient singularities.

Postgraduate on 26 October 2022 at 12:00
Speaker: Robin Visser (University of Warwick)
Title: Hilbert's Tenth Problem
Abstract: Can you find four distinct positive integers $w,x,y,z$ such that $w^3+x^3=y^3+z^3$ ?
If that's too easy, try finding a nontrivial integer solution to $x^4+y^4+z^4=w^4$.
And good luck finding any integral solution to $x^3+y^3+z^3=114$.
This all begs the question of whether we can construct a general algorithm to determine whether any given Diophantine equation has integer solutions. David Hilbert posed this exact question at the second ICM in 1900, where a negative answer was finally proven 70 years later by Yuri Matiyasevich building on work by Martin Davis, Hilary Putnam and Julia Robinson. In this talk, we'll explore the mathematical ideas behind Hilbert's tenth problem as well as go over many surprising applications, extensions to other number fields, and how this relates to several other famous open problems! 
Algebraic Topology on 25 October 2022 at 16:00
Speaker: Severin Bunk (Oxford)
Title: Functorial field theories from differential cocycles
Abstract: In this talk I will demonstrate how differential cocycles give rise to (bordismtype) functorial field theories (FFTs). I will discuss some background on smooth FFTs, differential cohomology and higher gerbes with connection as a geometric model for differential cocycles before explaining the general principle for how to obtain smooth FFTs from higher gerbes. In the second part, I will focus on the twodimensional case. Here I will present a concrete, geometric construction of twodimensional smooth FFTs on background manifolds, starting from gerbes with connection. This is related to WZW theories. If time permits, I will comment on an extension of this construction which produces openclosed field theories.

Ergodic Theory and Dynamical Systems on 25 October 2022 at 14:00
Speaker: Maryam Hosseini (Open University)
Title: About Minimal Dynamics on the Cantor Set
Abstract: Dimension group is an operator algebraic object related to minimal dynamical systems on the Cantor set. In this talk after a quick review of some definitions of dimension group, the {\it topological and algebraic rank} of Cantor minimal systems are considered and we will see how the rank of a Cantor system is dominated by the rank of its extensions.

Partial Differential Equations and their Applications on 25 October 2022 at 12:00
Speaker: Alexandra Tzella (University of Birmingham)
Title: TBA
Abstract: TBA

Algebra on 24 October 2022 at 17:00
Speaker: Alexandre Zalesski (UEA)
Title: Some problems on representations of simple algebraic groups
Abstract: Some open questions on the weight structure of tensordecomposable representations of simple algebraic groups will be discussed.

Number Theory on 24 October 2022 at 15:00
Speaker: Aleksander Horawa (Oxford)
Title: Motivic action on coherent cohomology of Hilbert modular varieties
Abstract: A surprising property of the cohomology of locally symmetric spaces is that Hecke operators can act on multiple cohomological degrees with the same eigenvalues. We will discuss this phenomenon for the coherent cohomology of line bundles on modular curves and, more generally, Hilbert modular varieties. We propose an arithmetic explanation: a hidden degreeshifting action of a certain motivic cohomology group (the Stark unit group). This extends the conjectures of Venkatesh, Prasanna, and Harris to Hilbert modular varieties.

Colloquium on 21 October 2022 at 16:00
Speaker: Pierre Raphael (Cambridge)
Title: Singularity formation for super critical waves
Abstract: Give a wave packet an initial energy and let it propagate in the whole space, then in the linear regime, the wave packet will scatter. But in non linear regimes, part of the energy may concentrate to form coherent non linear structures which propagate without deformation (solitons). And in more extreme cases singularities may form. Whether or not singular structures arise is a delicate problem which has attracted a considerable amount of works in both mathematics and physics, in particular in the super critical regime which is the heart of the 6Th Clay problem on singularity formation for three dimensional viscous incompressible fluids. For another classical model like the defocusing Non Linear Schrodinger equation (NLS), Bourgain ruled out in a breakthrough work (1994) the existence of singularities in the critical case, and conjectured that this should extend to the super critical one. I will explain how the recent series of joint works with Merle (IHES), Rodnianski (Princeton) and Szeftel (Paris 6) shades a new light on super critical singularities: in fact there exist super critical singularities for (NLS), and the new underlying mechanism is directly connected to the first description of singularities for three dimensional viscous compressible fluids.

Combinatorics on 21 October 2022 at 14:00
Speaker: Daniel Iľkovič (Masaryk University)
Title: Quasirandom tournaments
Abstract: A directed graph H is quasirandomforcing for tournaments if the limit (homomorphic) density of H in a sequence of tournaments is 2^−E(H) if and only if the sequence is quasirandom. The cyclic orientation of a cycle of length k is quasirandomforcing if and only if k = 2 mod 4. We study a generalization of this result: what orientations of a cycle of length k are quasirandomforcing? We show that no orientation of an odd cycle is quasirandomforcing and classify which orientations of even cycles of length up to 10 are quasirandomforcing. This is joint work with Andrzej Grzesik, Bartosz Kielak and Dan Kráľ

Applied Mathematics on 21 October 2022 at 12:00
Speaker: Francis Aznaran (Oxford)
Title: Finite element methods for the Stokes–Onsager–Stefan–Maxwell equations of multicomponent flow
Abstract: The Onsager framework for linear irreversible thermodynamics provides a thermodynamically consistent model of mass transport in a phase consisting of multiple species, via the Stefan–Maxwell equations, but a complete description of the overall transport problem necessitates also solving the momentum equations for the flow velocity of the medium. We derive a novel nonlinear variational formulation of this coupling, called the (Navier–)Stokes–Onsager–Stefan–Maxwell system, which governs molecular diffusion and convection within a nonideal, singlephase fluid composed of multiple species, in the regime of low Reynolds number in the steady state. We propose an appropriate Picard linearisation posed in a novel Sobolev space relating to the diffusional driving forces, and prove convergence of a structurepreserving finite element discretisation. This represents some of the first rigorous numerics for the coupling of multicomponent molecular diffusion with compressible convective flow. The broad applicability of our theory is illustrated with simulations of the centrifugal separation of noble gases and the microfluidic mixing of hydrocarbons. This is joint work with Alexander VanBrunt.

Analysis on 20 October 2022 at 16:00
Speaker: John Lott (Berkeley)
Title: Two aspects of scalar curvature
Abstract: 

Geometry and Topology on 20 October 2022 at 14:00
Speaker: Henry Bradford (Cambridge)
Title: TBA
Abstract: TBA

Algebraic Geometry on 19 October 2022 at 15:00
Speaker: Nivedita Viswanathan (Loughborough)
Title: On the Rationality of FanoEnriques Threefolds
Abstract: There has been a lot of development recently in understanding the existence of KahlerEinstein metrics on Fano manifolds due to the YauTianDonaldson conjecture, which gives us a way of looking at this problem in terms of the notion of Kstability. In particular, this problem is solved in totality for smooth del Pezzo surfaces by Tian. For del Pezzo surfaces with quotient singularities, there are partial results. In this talk, we will consider singular del Pezzo surfaces which are quasismooth, wellformed hypersurfaces in weighted projective space, and understand what we can say about their Kstability. This is ongoing joint work with InKyun Kim and Joonyeong Won.

Postgraduate on 19 October 2022 at 12:00
Speaker: Ruzhen Yang (University of Warwick)
Title: Beilinson spectral sequence and its reverse problems on PP^2
Abstract: Derived category is widely accepted as the natural environment to study homological algebra. We will study the structure of the bounded derived category of coherent sheaves on projective space via the semiorthogonal decomposition (based on the Beilinson's theorem) and comparison (by a theorem by A. Bondal). As an example, we will give explicit free resolutions of some sheaves on P2 using the Beilinson spectral sequence. We will also discuss the reverse problem where we give a condition to when the complex given by the spectral sequence is a resolution of the ideal sheaf of three points.

Algebraic Topology on 18 October 2022 at 16:00
Speaker: Thomas Read (Warwick)
Title: Gtypical Witt vectors with coefficients and the norm
Abstract: The norm is an important construction on equivariant spectra, most famously playing a key role in the work of Hill, Hopkins and Ravenel on the Kervaire invariant one problem. Witt vectors are an algebraic construction first used in Galois theory in the 1930s, but later finding applications in stable equivariant homotopy theory. I will describe a new generalisation of Witt vectors that can be used to compute the zeroth equivariant stable homotopy groups of the norm $N_e^G Z$, for $G$ a finite group and $Z$ a connective spectrum.

Ergodic Theory and Dynamical Systems on 18 October 2022 at 14:00
Speaker: Joe Thomas (Durham University)
Title: Poisson statistics, short geodesics and small eigenvalues on hyperbolic punctured spheres
Abstract: For hyperbolic surfaces, there is a deep connection between the geometry of closed geodesics and their spectral theoretic properties. In this talk, I will discuss recent work with Will Hide (Durham), where we study both sides of this relationship for hyperbolic punctured spheres. In particular, we consider WeilPetersson random surfaces and demonstrate Poisson statistics for counting functions of closed geodesics with lengths on scales 1/sqrt(number of cusps), in the large cusp regime. Using similar ideas, we show that typical hyperbolic punctured spheres with many cusps have lots of arbitrarily small eigenvalues. Throughout, I will contrast these findings to the setting of closed hyperbolic surfaces in the large genus regime.

Algebra on 17 October 2022 at 17:00
Speaker: Kamilla Rekvényi (Imperial College London)
Title: The Orbital Diameter of Primitive Permutation Groups
Abstract: Let G be a group acting transitively on a finite set Ω. Then G acts on ΩxΩ component wise. Define the orbitals to be the orbits of G on ΩxΩ. The diagonal orbital is the orbital of the form ∆ = {(α, α)α ∈ Ω}. The others are called nondiagonal orbitals. Let Γ be a nondiagonal orbital. Define an orbital graph to be the nondirected graph with vertex set Ω and edge set (α,β)∈ Γ with α,β∈ Ω. If the action of G on Ω is primitive, then all nondiagonal orbital graphs are connected. The orbital diameter of a primitive permutation group is the supremum of the diameters of its nondiagonal orbital graphs. There has been a lot of interest in finding bounds on the orbital diameter of primitive permutation groups. In my talk I will outline some important background information and the progress made towards finding explicit bounds on the orbital diameter. In particular, I will discuss some results on the orbital diameter of the groups of simple diagonal type and their connection to the covering number of finite simple groups. I will also discuss some results for affine groups, which provides a nice connection to the representation theory of quasisimple groups.

Number Theory on 17 October 2022 at 15:00
Speaker: Maria Rosaria Pati (Padova)
Title: Linvariants for cohomological representations of PGL(2) over an arbitrary number field
Abstract: In this talk I will construct the automorphic Linvariant attached to a cuspidal representation π of PGL(2) over an arbitrary number field F, and a prime p of F such that the local component πp is the Steinberg representation and π is noncritical at p. I will show that, if F is totally real then the automorphic Linvariant attached to π and p agrees with the derivatives of the Upeigenvalue of the padic family passing through π. From this I will deduce the equality between the automorphic Linvariant and the FontaineMazur Linvariant of the associated Galois representation. This is a joint work with Lennart Gehrmann.

Colloquium on 14 October 2022 at 16:00
Speaker: David Rand (Warwick)
Title: An appreciation of Christopher Zeeman
Abstract: In writing a biographical memoir of Zeeman for the Royal Society, I appreciated even more what a remarkable character he was, both in terms of his life, his leadership, his mathematics and his breadth of interests. I discovered a number of aspects that I don't think are very well known about his life and his contributions to topology, catastrophe theory and our department. In this colloquium I will try and give an overview of this.

Combinatorics on 14 October 2022 at 14:00
Speaker: Candy Bowtell (University of Warwick)
Title: The nqueens problem
Abstract: The nqueens problem asks how many ways there are to place n queens on an n x n chessboard so that no two queens can attack one another, and the toroidal nqueens problem asks the same question where the board is considered on the surface of a torus. Let Q(n) denote the number of nqueens configurations on the classical board and T(n) the number of toroidal nqueens configurations. The toroidal problem was first studied in 1918 by Pólya who showed that T(n)>0 if and only if n is not divisible by 2 or 3. Much more recently Luria showed that T(n) is at most ((1+o(1))ne^{3})^n and conjectured equality when n is not divisible by 2 or 3. We prove this conjecture, prior to which no nontrivial lower bounds were known to hold for all (sufficiently large) n not divisible by 2 or 3. We also show that Q(n) is at least ((1+o(1))ne^{3})^n for all natural numbers n which was independently proved by Luria and Simkin and, combined with our toroidal result, completely settles a conjecture of Rivin, Vardi and Zimmerman regarding both Q(n) and T(n). In this talk we'll discuss our methods used to prove these results. A crucial element of this is translating the problem to one of counting matchings in a 4partite 4uniform hypergraph. Our strategy combines a random greedy algorithm to count `almost' configurations with a complex absorbing strategy that uses ideas from the methods of randomised algebraic construction and iterative absorption. This is joint work with Peter Keevash.

Applied Mathematics on 14 October 2022 at 12:00
Speaker: Philip Herbert (HeriotWatt)
Title: Shape optimisation with Lipschitz functions
Abstract: In this talk, we discuss a novel method in PDE constrained shape optimisation. We begin by introducing the concept of PDE constrained shape optimisation. While it is known that many shape optimisation problems have a solution, their approximation in a meaningful way is nontrivial. To find a minimiser, it is typical to use first order methods. The novel method we propose is to deform the shape with fields which are a direction of steepest descent in the topology of W^1_\infty. We present an analysis of this in a discrete setting along with the existence of directions of steepest descent. Several numerical experiments will be considered which compare a classical Hilbertian approach to this novel approach.

Geometry and Topology on 13 October 2022 at 14:00
Speaker: Claudio Llosa Isenrich (KIT)
Title: Finiteness properties, subgroups of hyperbolic groups and complex hyperbolic lattices
Abstract: Hyperbolic groups form an important class of finitely generated groups that has attracted much attention in Geometric Group Theory. We call a group of finiteness type $F_n$ if it has a classifying space with finitely man cells of dimension at most n, generalising finite presentability, which is equivalent to type $F_2$. Hyperbolic groups are of type $F_n$ for all $n$ and it is natural to ask if their subgroups inherit these strong finiteness properties. We use methods from complex geometry to show that every uniform arithmetic lattice with positive first Betti number in $PU(n,1)$ admits a finite index subgroup, which maps onto the integers with kernel of type $F_{n1}$ and not $F_n$. This answers an old question of Brady and produces many finitely presented nonhyperbolic subgroups of hyperbolic groups. This is joint work with Pierre Py.

Algebraic Topology on 11 October 2022 at 16:00
Speaker: Sebastian Chenery (University of Southampton)
Title: On PushoutPullback Fibrations
Abstract: We will discuss recent work inspired by a paper of Jeffrey and Selick, where they ask whether the pullback bundle over a connected sum can itself be homeomorphic to a connected sum. We provide a framework to tackle this question through classical homotopy theory, before pivoting to rational homotopy theory to give an answer after taking based loop spaces.

Ergodic Theory and Dynamical Systems on 11 October 2022 at 14:00
Speaker: Sabrina Kombrink (University of Birmingham)
Title: TBA
Abstract: TBA

Algebra on 10 October 2022 at 17:00
Speaker: Gareth Tracey (University of Warwick)
Title: Primitive amalgams and the GoldschmidtSims conjecture
Abstract: The Classification of Finite Simple Groups has led to substantial progress on deriving sharp order bounds in various natural families of finite groups. One of the most wellknown instances of this is Sims' conjecture, which states that a point stabiliser in a primitive permutation group has order bounded in terms of its smallest nontrivial orbit length (this was proved by Cameron, Praeger, Saxl and Seitz using the CFSG in 1983). In the meantime, Goldschmidt observed that a generalised version of Sims' conjecture, which we now call the \emph{GoldschmidtSims conjecture}, would lead to important applications in graph theory. In this talk, we will describe the conjecture, and discuss some recent progress. Joint work with L. Pyber.

Number Theory on 10 October 2022 at 15:00
Speaker: Lambert A'Campo (Oxford)
Title: Galois representations and cohomology of congruence subgroups
Abstract: In this talk I will explain what it means to attach Galois representations to the cohomology of arithmetic locally symmetric spaces arising from congruence subgroups. In the case of GL(2) over imaginary CM fields (the method also works for GL(n)) I will explain how to prove, under certain conditions, that the Galois representations constructed by Harris–Lan–Taylor–Thorne and Scholze have good padic Hodge theoretic properties.

DAGGER on 10 October 2022 at 14:00
Speaker: Marco Linton (University of Oxford)
Title: Poison subgroups for hyperbolic groups
Abstract: It is a wellknown result that hyperbolic groups cannot contain certain `poison' subgroups. A lot of progress has been made towards understanding when the converse to this statement also holds. This includes several positive results, but also several negative results. In this talk, I will introduce hyperbolic groups, discuss some of these results and present the current state of the art for the class of onerelator groups.

Colloquium on 07 October 2022 at 16:00
Speaker: Michela Ottobre (HeriotWatt)
Title: Interacting Particle systems and (Stochastic) Partial Differential equations: modelling, analysis and computation
Abstract: The study of Interacting Particle Systems (IPSs) and related kinetic equations has attracted the interest of the mathematics and physics communities for decades. Such interest is kept alive by the continuous successes of this framework in modelling a vast range of phenomena, in diverse fields such as biology, social sciences, control engineering, economics, game theory, statistical sampling and simulation, neural networks etc. While such a large body of research has undoubtedly produced significant progress over the years, many important questions in this field remain open. We will (partially) survey some of the main research directions in this field and discuss open problems.

Combinatorics on 07 October 2022 at 14:00
Speaker: Mustazee Rahman (University of Durham)
Title: Suboptimality of local algorithms for optimization on sparse graphs
Abstract: Suppose we want to find the largest independent set or maximal cut in a large yet sparse graph, where the average vertex degree is constant. These are two basic optimization problems relevant to both theory and practice. For typical, or rather random sparse graphs, many algorithms proceed by way of local decision rules. Examples include Glauber dynamics, Belief propagation, etc. I will explain a form of local algorithm that captures many of these. I will then explain how they fail to find optimal independent sets or cuts once the average degree of the graph gets large. Along the way, we will find connections to entropy and spin glasses.

Analysis on 06 October 2022 at 16:00
Speaker: Murat Akman (Essex)
Title: Perturbations of elliptic operators on domains nonsmooth boundaries
Abstract: 

Geometry and Topology on 06 October 2022 at 14:00
Speaker: Grace Garden (University of Sydney)
Title: Earthquakes on the oncepunctured torus
Abstract: We study earthquake deformations on Teichmüller space associated with simple closed curves of the oncepunctured torus. We describe two methods to get an explicit form of the earthquake deformation for any simple closed curve. The first method is rooted in hyperbolic geometry, the second representation theory. The two methods align, providing both a geometric and an algebraic interpretation of the earthquake deformations. Pictures are given for earthquakes across multiple coordinate systems for Teichmüller space. Two families of curves are used as examples. Examining the limiting behaviour of each gives insight into earthquakes about measured geodesic laminations, of which simple closed curves are a special case.

Algebra on 05 October 2022 at 16:17
Speaker: Matija Vidmar (University of Ljubljana)
Title: Noise Boolean algebras: classicality, blackness and spectral independence
Abstract: Informally speaking, a noise Boolean algebra is an aggregate of pieces of information, subject to statistical independence properties relative to an underlying notion of chance. More formally, it is a distributive sublattice of the lattice of all subsigmafields of a given probability space, each element of which admits an independent complement. A noise Boolean algebra is classical (resp. black) when all its random variables are stable (resp. sensitive) under infinitesimal perturbations of its basic ingredients. For instance, the Wiener and Poisson noises are classical, but certain noises of percolation and coalescence are black. We shall see that classicality and blackness are respectively characterized by existence and nonexistence of certain socalled spectral independence probabilities that we shall introduce. Associated preprint: https://drive.google.com/file/d/1cLOHpHG_xgqPYmsbVIQmmYx08pqk4H6m/view

Postgraduate on 05 October 2022 at 12:00
Speaker: Sunny Sood (University of Warwick)
Title: Homological stability for $O_{n,n}$
Abstract: Motivated by Hermitian KTheory, we study the homological stability of the split orthogonal group $O_{n,n}$. Specifically, let $R$ be a commutative local ring with infinite residue field such that $2 \in R^{*}$. We prove that the natural homomorphism $H_{k}(O_{n,n}(R) ; \mathbb{Z}) \rightarrow H_{k}(O_{n+1,n+1}(R); \mathbb{Z})$ is an isomorphism for $k \leq n1$ and surjective for $k \leq n$. This will be an excellent opportunity to introduce esoteric concepts such as group homology and hyperhomology spectral sequences at the postgraduate seminar. This is all joint work with my supervisor Dr Marco Schlichting.

Partial Differential Equations and their Applications on 04 October 2022 at 12:00
Speaker: Tobias Barker (University of Bath)
Title: A quantitative approach to the Navier–Stokes equations
Abstract: ecently, Terence Tao used a new quantitative approach to infer that certain ‘slightly supercritical’ quantities for the Navier–Stokes equations must become unbounded near a potential blowup time. In this talk I’ll discuss a new strategy for proving quantitative bounds for the Navier–Stokes equations, as well as applications to behaviours of potentially singular solutions. This talk is based upon joint work with Christophe Prange (CNRS, Cergy Paris Université).

Number Theory on 03 October 2022 at 15:00
Speaker: Matteo Tamiozzo (Warwick)
Title: Perfectoid quaternionic Shimura varieties and the Jacquet–Langlands correspondence
Abstract: The Hodge–Tate period map can be thought of as a padic analogue of the Borel embedding. However, unlike its complex counterpart, it is not injective, and the pushforward of the constant sheaf via the Hodge–Tate period map encodes interesting arithmetic information. In the setting of quaternionic Shimura varieties, I will explain the relation between the structure of this complex of sheaves and level raising and the Jacquet–Langlands correspondence. I will then discuss applications to the study of the cohomology of quaternionic Shimura varieties. I will illustrate most of the arguments in the simplest setting of modular and Shimura curves. This is joint work with Ana Caraiani.

DAGGER on 03 October 2022 at 14:00
Speaker: Aleksi Pyörälä (University of Oulu)
Title: Normal numbers in selfconformal sets
Abstract: During recent years, the prevalence of normal numbers in natural subsets of the reals has been an active research topic in fractal geometry. The general idea is that in the absence of any special arithmetic structure, almost all numbers in a given set should be normal, in every base. In our recent joint work with Balázs Bárány, Antti Käenmäki and Meng Wu we verify this for selfconformal sets on the line. The result is a corollary of a uniform scaling property of selfconformal measures: roughly speaking, a measure is said to be uniformly scaling if the sequence of successive magnifications of the measure equidistributes, at almost every point, for a common distribution supported on the space of measures. Dynamical properties of these distributions often give information on the geometry of the uniformly scaling measure.

Analysis on 23 June 2022 at 16:00
Speaker: Matthew Hyde (Warwick)
Title: Quantitative rectifiability and the ddimensional Analyst's Travelling Salesman Theorem
Abstract: 

Analysis on 16 June 2022 at 16:00
Speaker: Jonathan Hickman (Edinburgh)
Title: The helical maximal function
Abstract: 

Analysis on 10 June 2022 at 14:00
Speaker: Yannick Sire (Johns Hopkins)
Title: Some results on harmonic maps with free boundary and beyond
Abstract: 

Analysis on 09 June 2022 at 16:00
Speaker: Giuseppe Tinaglia (KCL)
Title: A structure theorem for properly embedded CMC surfaces of finite genus and applications
Abstract: 

Analysis on 07 June 2022 at 16:00
Speaker: Luboš Pick (Charles University)
Title: Sharp transfer of regularity for the OrnsteinUhlenbeck equation
Abstract: 

Analysis on 26 May 2022 at 16:00
Speaker: Luc Nguyen (Oxford)
Title: Solutions to the sigma_kLoewnerNirenberg problem are not differentiable
Abstract: 

Analysis on 19 May 2022 at 12:00
Speaker: Juan Davila Bonczos (Bath)
Title: Blowup in infinite time for the KellerSegel system
Abstract: 

Analysis on 10 May 2022 at 16:00
Speaker: Neshan Wickramasekera (Cambridge)
Title: Meancurvature controlled codimension 1 integral varifolds near higher multiplicity hyperplanes
Abstract: 

Analysis on 05 May 2022 at 16:00
Speaker: Costante Bellettini (UCL)
Title: Hypersurfaces with prescribedmeancurvature: existence and properties
Abstract: 

Analysis on 17 March 2022 at 16:00
Speaker: Krzysztof Ciosmak (Oxford)
Title: Towards multidimensional localisation
Abstract: 

Analysis on 10 March 2022 at 16:00
Speaker: Julian Scheuer (Cardiff)
Title: Stability from rigidity via umbilicity
Abstract: 

Analysis on 03 March 2022 at 16:00
Speaker: Ovidiu Munteanu (University of Connecticut)
Title: Comparison results for complete noncompact threedimensional manifolds
Abstract: 

Analysis on 27 January 2022 at 16:00
Speaker: Annina Iseli (MSRI)
Title: Projection theorems for linearfractional families of projections
Abstract: 

Analysis on 20 January 2022 at 16:00
Speaker: Sylvester ErikssonBique (Oulu)
Title: A Sobolev differential structure and approximations of Sobolev functions
Abstract: 

Analysis on 09 December 2021 at 16:00
Speaker: Huy The Nguyen (QMUL)
Title: Noncompact selfshrinkers for mean curvature flow with arbitrary genus
Abstract: 

Analysis on 25 November 2021 at 16:00
Speaker: John MacKay (Bristol)
Title: Conformal dimension and decompositions of hyperbolic groups
Abstract: 

Analysis on 11 November 2021 at 16:00
Speaker: Daniele Semola (Oxford)
Title: Geometric measure theory on non smooth spaces with lower Ricci curvature bounds
Abstract: 

Analysis on 26 October 2021 at 16:00
Speaker: Melanie Rupflin (Oxford)
Title: Lojasiewicz inequalities for the harmonic map energy near simple bubble trees
Abstract: 

Analysis on 14 October 2021 at 16:00
Speaker: Ben Sharp (Leeds)
Title: Qualitative bounds on genus and area for embedded CMC surfaces
Abstract: 